Poutineville is hands-down my favourite poutine place in Montreal! However, make sure you are ordering POUTINE and not something else (you wouldn't go eat vegetables at an bbq restaurant).
This being said, I highly recommend their build your own poutine option and even more highly recommend their smashed potatoes - they are so crunchy on the outside and soft on the inside, even when covered with gravy. Also, make sure you stick with the cheese curds and do not change it to any other kinds of cheeses (poutine isn't poutine without the curds).
I usually build mine with smashed potatoes, regular gravy and cheese and top up with two vegetables and one protein (I find hot-dog sausages particularly good in poutine - they are normal processed hotdog sausages). Oh and I always make sure to add onions!