Also worth noting that TK release their inventory earlier than AC do - you may find more success if you book this as YVR-YUL-IST-YUL, open-jaw, and then go back later and add the YUL-YVR leg for a $90 change fee.

Downside is the $90 change fee, upside is locking in the sought-after TK seats (if you're looking for business-class tickets), but for an October-November trip I can't see the TK seats getting snapped up in the month or so until AC release their Nov 2015 avails.

Is Istanbul your destination, or are you heading anywhere else? I ask because IST is just outside the Europe 1 zone, and so costs more miles than if you're using IST to connect on to somewhere else in Europe.