This is insane. Your insights and analysis are good - this crosses the rubicon. There would be no way for either country to move past this suggestion. Self serving at best.
If Canadian politicians actually had guts, they would cut off Canadian crude exports to the US.
It would hurt Canadian oil producers temporarily, but US commercial crude inventories would hit tank bottom in 2 weeks (4 million b/d x 14 days = 56 million bbls).
And yes, Canadian crude imports are that important for the US.
But they wonโt do it, so donโt worry.