Montreal Airport has one fairly large, well-organised terminal divided into domestic, international and US flights.
However, everything is located in one building and the distances between the sections are short (within a 10-minute walk).
Immigration and security checks
Montreal Airport has efficient security and immigration controls.
Security checkpoints usually have queues of up to 20 minutes, and immigration screening upon arrival is largely automated and usually takes 10-20 minutes.
Current queue times can be viewed on the airport's official website: admtl.com/estimated-wait-time.
Transfer between flights
Montreal is a bit friendlier than the larger Toronto airport for transfers. You never have to change buildings because Montreal Airport has only one terminal.
Do I have to go through immigration to pick up my luggage?
Canadian airports, unlike those in the US, have a separate transit area.
If you change planes in Montreal in one booking, your airline will likely check your bags through to your final destination, so you don't have to enter Canada at all - you stay in the transit zone.
Of course, this only applies if you are transferring from an international to an international flight. If you are transferring to a domestic flight within Canada, you must go through immigration. However, the airline can still send your luggage to your final destination, it is always case by case.
You must always pick up your luggage and re-check it when you change from an international flight to a domestic flight.
There is an advance US immigration checkpoint at Toronto Airport, so if you are connecting in Toronto for a flight to the US, you will not need to go through immigration once you arrive in the US.
Do I need an eTA?
Even if you are only transferring from an international flight to an international flight, you must obtain an eTA to enter Canada. It can be done conveniently online for a fee at 7 cad.
For the complete transfer procedures, please visit the airport's website: admtl.com/connecting-flights