Your luggage is lost, damaged or delayed? You should immediately report the situation to your airline which is responsible for checked baggage from the check-in counter to the baggage carousel at destination, including delivery of the aircraft to the carousel.
If your airline confirms to you that your luggage is at YUL and you wish to take possession of it yourself, you can always come to the airport. However, be sure to ask your airline for their hours of operation. When you arrive, go to doors 28 at the arrivals level. Phones are in front of doors 28. Follow the instructions on the black phones and an agent will answer you and tell you how to pick up your luggage.