If you love Mont Tremblant, you wouldn't want F1 there. The track is not up to F1 standard, and bringing it up would destroy all of its character. I'd hate to see that happen to such a wonderful circuit. Plus, of course, the people in the area are already trying to get it shut down because of the "noise."
Same goes for Mosport (minus the noise part, afaik).
3 Rivers wasn't good enough for Champ Car, doubt it'll be good enough for F1. Plus, it's not a particularly brilliant circuit anyways.