From the Airport to McGill/Sofitel:
You will take the 747 Express Bus from YUL to Berri-UQAM Station (corner of St. Catherine and Berri-UQAM), and then you will take the Metro in the direction of Angrignon and you will go four stops, exiting at Boulevard Robert-Bourassa. You will then walk toward McGill College street, turning right on McGill College toward the university. McGill College ends at McGill (the actual university), so you can’t miss it. You will cross Sherbrooke (McGill University is on the north side of Sherbrooke), turn left (which is west) and go two blocks to the Sofitel, which is on the same side of the street as McGill (North side).
Here are two links. The first is the Bus link, the second the Metro link.
View express and city bus routes, schedules, fares and points of sale.