The best chocolate Souffle I had in Montreal is at Taverne in the Square in Westmount. It takes 15 min to prepare so I usually order it before the end of my meal. Its not cheap! delicious though... Maybe $9 -$11. The food is also really good if you haven't been. Taverne in the square is also one of my favorite neighborhood dinner restaurants. I love sitting on the terrace in the summer.
Taverne Sur Le Square
1 Carré Westmount, Westmount, QC
I also had a really good chocolate souffle at Juliette et Chocolat. It still wasn't as good as the one at the Taverne.
At the Metro in Westmount and Victoria I bought these little chocolate lava Souffle you just pop in the oven. I was surprised, they were incredible!!