I was once in a very similar situation, flying CDG-LHR on AF, then LHR-YOW-YUL on AC. I initially was supposed to have about 3 hours between flights at LHR. AF had oversold the flight out to LHR and put me on the following flight, which left more than 2 hours later, giving me about 40 minutes to change terminalsa t LHR, go through security and board the YOW flight. Virtually impossible. I sprinted out of the plane when we landed (actually reaching a door that hadn't yet been opened and banging into it). When I got to the AC counter at the right terminal they informed me that the YOW flight's doors were already closed. I was on a heavily discounted ticket, so I did not expect what came next: AC put me on the direct LHR-YUL flight (which left some 20 minutes later), and got a taxi to take me to the gate along the runways. I made it to YUL early, and with a compensation package from AF for the delay.

I would like to think that you can count on such service from AC, but unfortunately they have shown to be quite inconsistent, and so I wouldn't base a decision on their being as lenient as they were that day.