Montreal Airport – YUL
Montreal is serviced by Pierre Elliot Trudeau International Airport — YUL, located in Dorval, a suburb, about a 30min drive from Downtown (longer in bad traffic).
Ground transport
The Airport Bus is the key form of ground transport for many but costs $10, so if you're not travelling alone, then taking a taxi from the airport to any point Downtown at the $40 flat rate may be better for the extra speed and convenience.
US Immigration
Note that if you're flying from Montreal to the United States, U.S. Customs and Immigrations is handled in Montreal, so check-in at least 45 minutes earlier than you would usually would; longer if your visa status is complicated.