My experience a few years ago.
If you haven't applied for non-residence status in taxation in Canada, you need to file tax in both Canada and US.
You file tax first in Canada, and usually, the Canadian tax is way more than US. Then you file in US, and the tax you paid in Canada is counted as Foreign Tax credit, which is way more than the amount you owe to US. As a result you don't have to pay anything extra in US. But you have filed tax in both US and Canada, so you are legal to enjoy the legal status and benefit in both country.
If you've already filed non-residence status in taxation in Canada, you only need to file tax in US. (Big savings, BTW).
Again, this was a few years ago, so use it as a reference to do more research. Good luck.
