Economy

Raising the cost of any source eg. via a tariff on Canadian oil, would cause a change in suppliers to a cheaper source.

The cost of oil (over simplified but still complex...) is the cost of extraction + the cost of transport to refinery + the cost of refining (varies with the quality of the crude) + cost of transport to end users.

Sweet light Texas crude is right next to US refineries and true to its name is fairly easy and inexpensive to refine. Brent is a notch or two more expensive to refine and has to be shipped from north England, and Tar Sands (Alberta) oil only pumps when prices are very high because it is very expensive to refine. Canada has better grades too but I'm just laying out the basic range of crude oil quality.

Transport is railcars and pipelines. A Congress critter who is very lucky in his stock picks recently bought CP (Canadian Pacific rail) in big quantities. It is a very boring stock. Range bound for 3 years or more, bouncing around between $70 and $84. Speculation is obvious that this Congress critter knows something, eg some reason why rail transport will be more profitable soon.

https://www.marketwatch.com/investing/stock/cp