Online
There are several different websites where landlords list rental units. The most popular are Facebook Marketplace, Kijiji, LesPAC, Centris and DuProprio.
“For Rent” signs
Some landlords advertise an available apartment by posting a sign in front of the building or in the window of the rental unit.
You can find these signs by taking a walk around the municipality of your choice. They will usually have a phone number on them that you can call.