Hi Luc
I'm not really going to offer you any different advice for keeping your crickets alive then Zoe has already stated. I use about the same setup/food items as hers for my crickets.
I too live in Ottawa and I go through about 3000 crickets a week so I'm ordering in bulk from a supplier in Toronto and having them shipped in. When my collection was smaller, and was getting about 100 bugs a week, I too had a problem finding decent, healthy crickets here in town. What I did at the time was find out from the pet store what days they had their crickets delivered and go there and buy them that day or the next day to ensure I got them and they were "fresh".
If you would like, feel free to PM me for my opinions as to where to get the healthiest crickets in Ottawa. I don't want to get into a good pet store/bad pet store discussion on a public forum!
Hope this helps.
Trace