Boy, 90 minutes for a domestic-international connection is pretty tight, regardless of the airline and regardless of the fact that YWG is a small-ish airport. You'd have to check in with United, clear American-bound security, and go through customs pre-clearance...leaving not much wiggle room even with an on-time arrival on Calm Air. So while it may seem unfair, you really didn't give yourself a lot of breathing space in the first place.