I used OMW once for a XMas trip and I can tell you it came in handy as AC cancelled a slew of flights due to snowstorm.

The agent was good in providing accommodation and info on getting meals covered while I stayed overnight. As it was the start of my trip, they asked if I preferred taxi back home (and to the airport the next day), or a hotel. The rebooking had already been done when I went to check-in, but they also said they could check to see if there were other options for that evening.

OMW is booked based on one-way travel, so I assume YOW-YUL-LAX would be covered under the >1000 mile one-way trip cost of $35, but as Clipper801 suggested, best to check with AC.