Enter the Island via the 40, then exit Sources South...at rush hour, you might find it more advantageous to exit at Donegani/Cardinal and follow Cardinal East towards the airport, rather than get caught up in the Dorval Circle for the 20/520 interchange....although with the construction and the detours, getting to the Valet Parking next to the Sheraton may be tricky if not taking the Airport exit from the 520 (i.e. blockages on the thru-lanes and the round-about from Cardinal via Michel-Jasmin to come back to the airport entryway by the Sheraton). Hopefully your fare was worth it (or the destination difficult to get to otherwise) to take the 417 for 2hrs (hopefully not in a blizzard) and then park at YUL, rather than utilize YOW...