Canadian National Railway's Kingston Subdivision, or Kingston Sub for short, is a major railway line connecting Toronto with Montreal that carries the majority of CN traffic between these points. The line was originally the main trunk for the Grand Trunk Railway between these cities, although there has been some realignment of the route between these cities. The majority of the Kingston Sub runs close to the northern bank of Lake Ontario and the Saint Lawrence River.

The Grand Trunk Railway was a railway system that operated in the Canadian provinces of Quebec and Ontario and in the American states of Connecticut, Maine, Michigan, Massachusetts, New Hampshire, and Vermont. The railway was operated from headquarters in Montreal, Quebec, with corporate headquarters in London, United Kingdom. It cost an estimated $160 million to build. The Grand Trunk, its subsidiaries, and the Canadian Government Railways were precursors of today's Canadian National Railway.