orangesmile
Montreal itself is on an island. It is the 6th most populous island (>2 million) of the Americas and the 37th most populated island on Earth, outranking Manhattan Island in New York City.
Laval is on Île Jésus (Jesus Island), and has another 450,000 or so people. Then there are the smaller islands of the Hochelaga archipelago, including Grande-Île (~43,000), Ile Perrot (~40,000), Ile des Soeurs (~20,000), Ile Bizard (~15,000), and a 100 or so other islands, some populated.
Dorval Island (pop. 50) is Canada's smallest municipality.
https://en.wikipedia.org/wiki/L%27%C3%8Ele-Dorval
blogspot
there is also L'Île-Cadieux (pop ~110)
adjacent to Montreal and Laval are the Îles Laval (Notably Ile Bigras and Ile Pariseau), which have their own train connection to downtown Montreal.
wikipedia
and the site of Expo '67, which has its own metro station, Ile St. Helene and Ile Notre Dame:
greatruns