Hi Edward. Make sure it's unlocked. A phone won't work with other network if it's locked to a carrier. Here's Fizz FAQs for phone compatibility.
Here's an article that will help you with unlocking phones: The Complete Guide to Unlocking a Cell Phone
Heads up, if you're porting/transfering your number from Videotron to Fizz, don't cancel your account yet. Please don't cancel yet. Please let Fizz know or check out this guide. Hope that helps.