Im currently with cannet cable provider. If I switch to Fizz will there be some downtime?
There's no downtime. You can have both running at the same time. Once your Fizz connection is up and running, you can contact your other provider to cancel the old service.
See step 4 - https://fizz.ca/en/internet/how-it-works
Contact your previous provider to cancel your Internet subscription with them, and avoid paying double.