A FlyerTalk Posting Legend
Join Date: Sep 2012
Location: SFO
Programs: AC SE MM, BA Gold, SQ Silver, Bonvoy Tit LTG, Hyatt Glob, HH Diamond
Posts: 44,414
You can't have non-AC metal on short-haul redemptions.
As for whether it's valid, have you tried plugging it into Aeroplan.com?
There's nothing wrong with "backtracking" as long as you're within the mileage limitation. Going through YUL almost doubles the mileage, so I suspect that is the bigger issue.