We’ve flown AC a few times out of Montreal and they were fine. Just flew them last week to Athens. Plane needed a cosmetic overhaul (USB charging stations — multiple — literally falling out of the socket, touchscreens not fully functional, that type of stuff), meals were terribly small, but the FAs were courteous, professional, and helpful, the flight ran on time, and we got there safely. Mission accomplished.
I find them to be about the same as other carriers. Delta is our preferred airline; I think their customer service is better than others, including AC (in my experience). We fly with a disabled family member and we have a lot of “asks.” AC tries in theory, but it is sometimes a fight to get the seating, etc., that we need. Delta is a breeze.