I went to H&M to get some workout gears and I found what I was looking for in less than 30 minutes.
The main floor at the St-Catherine entrance, the second floor (1st actually) and the third floor are women and kids wear. The men section is at the bottom of the floor.
When I got the clothes I needed, I went to the dressing room. It was small but clean with enough light to look at yourself in the mirror. After my purchase, I went to the cash register to pay and I notice there is a donation box where you can put your used textile clothing and you get 5$ rebate on your next purchase at H&M. It is a great initiave!
Overall, their accessories section is extensive but I can't say much about the range of clothes. It seems like they are trying to pack every sort of styles in the same store with limited choices. The gym section has a small choices of outfits. I can't complain because I don't shop there very often but I felt they could do so much better giving their popularity.