CUN YYZ is the flight where AC screwed up my preferred seat. I wasn't walking normally getting off that plane after four hours.

I can't recall what J load was like, I do wonder if being a holiday destination and early July (possibly not peak season) the LMUs or a P fare would be reasonable. Because paying 10 credits for the whole lot is a great deal, but paying 10 credits and then potentially being waitlisted and never clearing YYZ YVR kinda sucks. Though being Comfort + SE hopefully your odds are decent. Good luck. I'd inquire about a OEN upfare on the YYZ YVR if it's a widebody (AC123 over AC121) to increase your odds though.