For some reason I think we can see Montreal in a day and a 1/2. In September would drive down from Quebec City probably arriving Montreal at around 2 PM. Have the rest of that day & night, and the following day & night. Only interested in heritage Montreal sights (not museums), and strolling heritage streets with shops and restaurants. Have been to many, many places and have found very, very few that warrant 3 or 4 or 5 days, as most local "experts" will say is necessary.
Prove to me that Montreal deserves more than a day and a 1/2!