You also say you're coming in from ORD, which means you'll be clearing immigration in YUL, and also waiting to pickup and transfer any checked baggage you may have. If you have Nexus, then you'll clear customs fast and just need to wait for your bag, but otherwise it all depends on how many flights are coming in. It's a Sunday, but it could take a bit.
Given that and re-clearing security... not worth it IMHO.