The US would probably laugh. . .

Seriosly though. Why do you think the US would be so worried about Quebec separation? If anything it would give western Canada more influence. And the west is distinctly more pro-American and closer to the American mindset than Quebec is. The change in balance of power could only help the US. The only downside might be economic issues. But even there I'm not entirely sure. Although clearly Quebec is doing vastly better now than during the last batch of separist rhetoric. (Which you'd think would tell the French nationalists something. . .)