Forever.
Although most of Canada's export goes to the USA, and about 50% of *that* is oil, the USA gets the same kind of bad crude from Venezuela.
And if they really had to, they could upgrade their refineries to use the light sweet crude produced in abundance in TX and is nearlly all exported.
It would also improve the USA's pollution situation dramatically.
But M Koch will be getting richer slower, and that will not be acceptable.