But the Grand Trunk Railway Company changed the original route of the T&G and extended the line to Sarnia, a hub for Chicago-bound traffic.

The explosive growth in trade during the 1850s within the United Province of Canada and further east by water to the Maritimes demanded that a railway link the entire geopolitical region.

Many citizens thought that the only way to finish the Grand Trunk – and protect the country – would be to unite all the colonies into a federation so that they could share the costs of an expanded railway system.

The end of the American Civil War saw British North America on the verge of uniting in a single federation, and the GTR's financial prospects improved as the railway was well-positioned to take advantage of increased population and economic growth.

[3] The GTR system expanded throughout southern Ontario, western Quebec, and the U.S. state of Michigan over the years by purchasing and absorbing numerous smaller railway companies, as well as building new lines.

GTR's largest purchase came on August 12, 1882, when it bought the 1,371-kilometre (852 mi) Great Western Railway, running from Niagara Falls to Toronto, and connecting to London, Windsor, and communities in the Bruce Peninsula.

By the early 20th century, GTR desired to operate in Western Canada, particularly given the virtual monopoly of service that CPR maintained and the lucrative increasing flows of immigrants west of Ontario.

GTR would build (with federal assistance) and operate the Grand Trunk Pacific Railway (GTPR) from Winnipeg, Manitoba to Prince Rupert, British Columbia, while the government would build and own the National Transcontinental Railway (NTR) from Winnipeg to Moncton, New Brunswick via Quebec City, which the GTR would also operate.

With the enormous cost of building the GTPR and the limited financial returns being realized, GTR defaulted on loan payments to the federal government in 1919.

GTR underwent serious financial difficulties as a result of the GTPR, and its shareholders, primarily in the United Kingdom, were determined to prevent the company from being nationalized as well.

Eventually on July 12, 1920, GTR was placed under control of another federal government Board of Management while legal battles continued for several more years.

Canada's worst railway accident based on loss of life happened on the GTR, occurring on June 29, 1864, when a passenger train operating between Lévis and Montreal missed a signal for an open drawbridge on the Richelieu River near the present-day town of Mont-Saint-Hilaire, Quebec, plunging onto a passing barge and killing 99 German immigrants.

[5] The GTR was a private company headquartered in England that received heavy Canadian government subsidies and was never profitable because of competition from shipping and American railways.

Sir Joseph Hickson was a key executive from 1874 to 1890 based in Montreal who kept it afloat financially and formed an alliance with the Conservative party.

Carlos and Lewis (1995) show that it managed to survive because its British investors accurately assessed the corporation's value and prospects, which included the likelihood that the Canadian government would bail out the railway should it ever default on its bonds.

He upgraded the tracks, bridges, shops and rolling stock, but was best known for building huge grain elevators and elaborate tourist hotels such as the Château Laurier in Ottawa.

in 1903 by building a subsidiary, the Grand Trunk Pacific Railway Company some 4,800 kilometres (3,000 mi) long; it reached Prince Rupert in northern British Columbia in 1914.

As a result, significant sections of GTR mainlines in Canada and Grand Trunk Western routes in the U.S. are still in active use by Canadian National (CN) today, particularly the Quebec City–Chicago corridor by way of Drummondville, Montreal, Kingston, Toronto, London, Sarnia/Port Huron, and Battle Creek.