I'm as usually not surprised to see the Montrealers have let the tourists write majority of the reviews about a signature building of the Old Port. Marché Bonsecours has a beautiful architecture and blends so well with the surroundings. It has been well reconstructed inside with the idea of multipurpose use. The main floor is occupied by little shops and it is true some of them are overpriced and can be called tourist traps, but indeed there are some beautiful Canadian items that are not necessarily souvenirs you can discover browsing around.
The locals don't come to Marché Bonsecours for their weekend shopping. They come because of the beautiful exhibition space at the bottom floor, entrance from rue de la Commune that overlooks Saint Laurence river. For few years now I have been frequenting the heartbreaking World Press photo exhibition in the very same hall. They come for special events organized at the third floor as Je t'aime en chocolat, small venue full of literally sweet joy. They come for the few pubs and cafes that use some of the market space. They come out of respect for the old historic building.
So, if you are wondering what to do this weekend go check the building for its architectural value, eat some chocolate and write an appreciative review in Yelp for Marché Bonsecours.