Planes take off and land into the wind so they don’t crash. Runways are built in the directions wind blows, and wind direction tends to be pretty consistant, so an airport’s runways often all face the same direction.
Some locations have very variable wind conditions so an airport may have runways in many different directions. For example, Wittman where they have Oshkosh has 4 runways in all different directions. http://img.airnav.com/aptdiag/w240/02539.gif?v=OY0UYO
Larger airports typically like to have more traffic throughput by having many parallel runways, like Atlanta which has all 5 runways facing east/west. This means planes may have to take off/land in crosswind conditions, which is not ideal but can be done. https://img.airnav.com/aptdiag/w240/02655.gif?v=Q88169
I have landed at ATL in a storm. I can confirm the first two points and the fact I can do so today confirms the last – but it was a bit of a code-brown!
Not from Montreal, but barring airport specific reasons to use specific runways (like terrain or noise abatement), which it doesn’t look like Trudeau does, it’s going to come down to wind direction or traffic flow etc.
For example right now it looks like there’s a 10kt headwind for runways taking off over the water so it would likely be preferred for takeoff barring the above.
