If you don't mind waiting a bit for your meal, this is probably the most legit Mexican food you'll find in Montreal. Each of the taco plates come in little casserole dishes with a basket of soft taco shells on the side, so unlike other taco joints, you have the ability to portion control. I got one order of the cactus tacos and another of the shrimp: both were superb, and ample for one person. Granted, I filled up on guacamole first, but you probably will too so we're cool.
Warning: these guys are not messing around with their hot sauce. Use it with caution.