Jean Talon Market
There are two large markets in Montreal -- Atwater and Jean Talon. There are also specialty markets (flowers only, for example) as well as neighborhood occasional markets. Montreal is a market kind of town.
If you love a good market, I would recommend Jean Talon. While a little farther afield than the more centrally located Atwater, Jean Talon is a larger market with a greater variety of flowers, veggies, breads, meats, cheeses, chocolates, etc. There are also restaurant stalls.
Jean Talon website: https://www.marchespublics-mtl.com/en/marches/jean-talon-market/
Located at 7070 Henri-Julien Avenue, Jean Talon is pretty easy to get to by metro (about a 7-minute walk from the Jean Talon metro stop).