I took a look at David's Bridal in Trainyards and have amazing service every time I go in, whether it's for bridesmaids dresses or accessories. I also visited Merry Mary's downtown. I ended up purchasing my dress on the Quebec side however; a friend's relative had a shop that closed down and she still has a lot of stock.
I shopped at Janine Adamyk in Ottawa. I have grown up peeking into her store window and dreaming of the day that I would get to go inside. It did not disappoint! Also, I recommended my best friend go there, and she had a really good experience! Good luck!