I do YYC-YUL a couple times a year, always on AC. I usually stay downtown.

This won't change my habits - AC to YUL it is.

What might sway me is if I can't consistently get preferred seats on AC. I don't check bags, OLCI, have nexus, don't use the MLL much, only get a few upgrades a year - so those seats matter to me. With AC's reconfigured narrowbodies, I'm worried there won't be enough of these, and I'll get stuck in regular Y. If that happens, I just won't see much benefit in flying AC. At that point, I'd be tempted to at least try the new airport with Porter.