Good idea, but did not work in this case because the YQB-YUL segment is all Y and it only prices the Y cabin. If I ask for J it says "no flights found."
Thanks for letting me know about google flights. I am sure I can use it in other instance...
Would also suggest using Google Flights, it let's you build some crazy multi-segment itineraries and prices it right through on ac.com
Since this only works for lowest Y booking class, I'd call in and feed the agent the exact flight numbers you want, as well as the booking class.
Can't see why this shouldn't work.