Agreed with the suggestions to look near the Passport Offices. I renewed my Passport on my last trip home, since it's much cheaper and easier than applying from the U.S..
I was able to get them done for $10 at a place within walking distance of the Guy-Favreau Complex Passport Office in Montreal, and they were accepted on the first try. Compared to my Mom's last attempt - she paid $10 at Pharmaprix (a.k.a. Shoppers Drug Mart outside of Quebec), but ended up having the photo rejected because it didn't meet the requirements.
I do hear Costco is both good and dirt cheap, but I think you need to have a membership or have a member go with you to pay.