I don't remember if AC operates YYZ or YUL to IST, but AP can generally open reward space on AC in the event of a schedule change. So if AC has a non-stop, you could get that, or if there's nothing on YYZ-CDG but there is space on CDG-IST, they could in theory open up space on YYZ-CDG, although I'm not sure they'd be more amenable to that than to opening space on YYZ-IST