the reason these pipelines don't exist is that there's no business case for them. alberta oil is high cost, dirty and low quality. we export it all to the united states because nobody else wants it. further, cutting supply to the united states will increase profits for venezuela and saudi arabia, and cut us out.
there's a saying about cutting one's nose off to spite one's face.
it's an utterly stupid idea.
the correct tactic is an export tax.