Since you started your post in the past tense, is this a trip you've already taken? If so, did you end up missing your connection?

From what I've been able to find, the minimum connecting time at YUL from an international flight to a Canadian flight is, in fact, 60 minutes. Just because you may miss your 2nd flight, that really doesn't prove any negligence by BA.

Did you buy this ticket without checking the connecting time? Since you seem to be familiar with the wait times in YUL, why didn't you choose another itinerary with a bit longer connection? You certainly aren't required to accept what BA offers. There are many times I've not chosen flights with the minimum connecting time since I didn't feel comfortable with them.

Also, just because 2 airlines are not in the same alliance doesn't mean they don't have an interline baggage agreement. I'd would guess 2 major carriers such as AC & BA do interline.