McGee at various times had made visits to the British colonies. He had delivered public lectures in Montreal. He had summered on Lake Huron, had written letters to his paper from the upper Ottawa, and had passed through the rich meadows and orchards of the Annapolis valley in Nova Scotia. At all times he was struck with the orderly and secure society of the British provinces, while his imagination had been kindled by the magnificent future which stretched before them. He early visualized them as the germ cells of a new nation. He was, therefore, prepared in 1857 to accept readily the invitation of some Canadian Irishmen to become their leader in Lower Canada. A delegation consisting of such prominent Irish Canadians of the period as Frank Smith, Patrick Brennan, and James Donnelly went to New York, interviewed McGee, and obtained his acceptance of their invitation. In the spring of 1857 he moved to Montreal, and there began his Canadian career.

To McGee British North America seemed on the threshold of a new and promising era. The steam-boat was drawing the provinces closer to Britain. The telegraph and Atlantic cable were making possible more intimate co-operation between the various provinces themselves, and between them and the mother country. The building of railways promised in the near future to bridge the dreary distances of forest and rock which severed the various colonies from one another and kept them as far apart as Europe is from America. In addition to these facts was another laden with rich hope, the prospective annexation to the Canadas of the vast hinterland then under the dominion of the Hudson's Bay Company. What are now the rolling wheat fields of Manitoba and Saskatchewan were in 1857 merely the hunting grounds of trappers, employed by one of the mightiest of British mercantile corporations. Yet there were some men who had caught a glimpse of the potential value of those extensive lands beyond Lake Superior. They described them as the natural field of expansion for the eastern colonies and advocated their annexation. Under the inspiration of these pregnant facts, McGee in May, 1857, established in Montreal a tri-weekly paper, called the New Era as indicative of the time of its birth.

The paper had too brief a career to exercise much influence on public life. Moreover, in 1857, McGee, as a newcomer, was of necessity feeling his way amid the shoals and narrows of Canadian politics, and was unable to discuss local issues with intimacy. None the less, the New Era has an outstanding significance in Canadian history. It was the first newspaper in the British colonies dedicated to the cause of colonial union and the establishment of a British American nationality under the rule of a royal prince. It advanced the chief arguments for union employed eight years later at the conferences of Charlottetown and Quebec. It pleaded an aspiration not finally realized for another ten years. To McGee nothing seemed more apparent than that the Canadas and the colonies by the sea should form the nucleus of a nation. The essential means was the development of a common will strong enough to overcome the obstacles in the way of closer co-operation.

The vision of a united British America was not new. It was as old as the existence of the colonies. It grew naturally out of the presence of a number of scattered communities whose common interests could best be served by a common government. Previous to the American Revolution the great Franklin had advocated such a union for the thirteen colonies. After the Revolution it found many champions in the territories which remained under the British crown. In 1790, while the Constitutional Act for the Canadian provinces was being fashioned, Chief Justice Smith suggested a plan for the comprehensive government of all the colonies. In the succeeding years, many others made similar suggestions—Uniacke in Nova Scotia, Sewell in Quebec, William Lyon Mackenzie, the fiery Canadian agitator, and John Beverley Robinson, an Upper Canadian who had pondered long and carefully on colonial issues. Even the distinguished name of Lord Durham was associated with the idea. He recommended it as the one means of developing for the colonies a British American nationality, which should rival the robust and aggressive nationality across the southern frontier.

After 1850, the conception was dragged into the daylight of practical politics. A number of prominent Canadians saw in it the one solvent of the constitutional difficulties arising from the Union Act of 1841. In April, 1856, A. A. Dorion, leader of the Lower Canadian Liberals, pleaded in parliament for the federal union of the two Canadas. Thus, the idea had already entered the stage of practical discussion when McGee established his New Era. But with the politicians it was entertained largely as a gateway of escape from the political embarrassments of the existing system, and was made subsidiary to party considerations. McGee in his paper fired it with a wider emotional appeal. With him it was not the product of close grappling with the political difficulties of the Union Act, but a poet's vision. It was a dream in the fulfilment of which lay a mighty future for all the peoples of British North America. With a newcomer's freshness of observation, he saw in the colonies possibilities of development which had lain largely unnoticed by the public men of the colonies. He thought as much of the social and spiritual consequences of union as of the political. It would not merely provide the British provinces with the strength of a common government, but would knit the scattered colonists into a united, self-reliant people, with a common will and common hopes, the true evidence of nationality. Union would carve the way for the emergence of a great new northern nation. It would provide the people with vision, and destroy the cramping parochialism of their existing political life.

In British American union, McGee at last discovered a cause that vividly appealed to his imagination. He found it on taking up residence in Montreal, and it shaped his career in the succeeding ten years. It replaced in his sentiments his former fervour for Irish liberty. In its advocacy he never grew weary, and the decade previous to Confederation found no more fervid apostle of British American union and nationality than McGee. He pleaded it, not merely through the press, but on the public platform. Being in demand as a lecturer, he used every occasion to unfold his favourite subject. In one of his most famous addresses, delivered at Ottawa on October 9, 1857, he arrayed the various arguments for union. "If we extend our vision so as to embrace all British North America, we survey a region larger than all Europe. If we have no coal, Nova Scotia has abundance. If Newfoundland has an indifferent soil, this Ottawa valley can grow wheat enough to supply all that is required. Throughout this wider view we find at least four millions already in the field—one quarter more than laid the neighbouring republic. Nature pronounces for the union of the provinces. Canada needs a sea-coast."

In addition to the arguments drawn from geography and economic needs were others no less cogent. Union was imperative for defence. Political weakness was always a tempting bait to a neighbouring power. The great resources of the British colonies combined with their lack of unity might well induce the American republic to attempt conquest. Especially was the St. Lawrence waterway tempting to the United States, since in the course of time it must become the shipping route for the wheat harvests of the West. The power in possession of it would control the chief roadway to the grain fields. In addition the colonies had other resources for which union alone could give adequate protection, rich fisheries, extensive forests, fertile lands. "Facts are logical, and unless we dream that the laws of cause and effect will be suspended in our favour, we must look either to the internal union or the political extinction of these provinces at no distant day." Not merely would the wealthy natural resources of British North America be preserved, but they would best be developed by the consolidation of the colonies into one state. With such a system McGee looked forward to Canada possessing, by the close of the century, 25,000,000 people. Moreover, he anticipated the appearance of all the other more brilliant, if less tangible, accomplishments of national life, which had difficulty in arising under the existing political disunion, a native literature, with developments in art, science, and philosophy.

McGee went further than marshalling arguments for union. He described in general terms the nature of the constitution suitable for the colonies. He considered it neither desirable nor possible that the various provinces with their diverse geographical characters and economic interests should be fused into one political unit. "Our river system indicates our union, railroads and canals will strengthen these natural bonds, but complete oneness of political life must still be wanting to sea-beaten Newfoundland and the wheat-bearing West." The same geographical facts which pressed the need of union made the recognition of local autonomy imperative. The new constitution must be federal, allowing a large measure of local autonomy, while constituting a central government to deal with common interests. Many of the leading Fathers of Confederation, most prominent among whom was Sir John A. Macdonald, began with the suggestion of a legislative union, and only with reluctance in the heat of constitution-building recognized the need of federal institutions. But with keen insight McGee saw from the outset that only federation could be the goal of British Americans. Provincial governments with the recognition of certain provincial rights would be a guarantee of liberty in the new state.

In December, 1857, an additional field was opened in which McGee might extend the advocacy of his new found cause. A body of citizens in Montreal nominated him for parliament, and in the ensuing contest he was elected as one of the three representatives of the city. Thus began the most constructive venture of his career.