We spent an entire week at Mark's place. The location is about a 15 minute walk to multiple metro stops. One street over from bars and restaurants. Super close walk (15-20 minutes) to the Old Port and most other attractions. Also, right near the base of the mountain.
The apartment is on the second story, so you must be able to walk up spiral stairs. We're planning to stay here again for future trips to Montreal! Mark made everything easy and was punctual for check-in and out.