I generally agree with your points, but I can assure you that the US does not import Canadian oil at a discount. Oil is a global commodity and is priced as such. Canadian heavy crudes like Cold Lake price lower than lighter crudes like WTI because of quality differential, and for no other reason. Refineries that can process heavy, sour Canadian crude (Pine Bend, Wood River), cost more than twice what a refinery capable of processing WTI costs. The crude is priced to reflect this.
My beef with Canada, and it’s a situation I tried hard to correct, is that no investment has been made to process these heavy crudes other than at Irving Oil’s Saint John refinery.
Interestingly, I did the initial economic analysis on that conversion as a young engineer at Irving.
If Canada was on their game, they would have encouraged the development of a heavy oil refinery in Hardisty, AB and converted the crude oil export lines to refined products. The trade game would be dramatically different if they had had the foresight to did so.
Sorry, probably way more information than you wanted.