What other networks do Fizz use for EXT coverage?

Vincent R. 156

I know they are mainly operating on Videotron network. But what other networks are they using? Bell, Telus, Rogers?

Allison W.

Rogers (videotron shares towers with them).

AlexB

Primarily Rogers, but if you're in an area where Rogers isn't available, it hops on to Bell or Telus.

FizzWiggler G.

Alexandre B is correct.
Most all Canadian operators have nationwide agreements with each other in order to offer full country-wide coverage.
No matter your provider, you'll find an area of the country where you phone says EXT for extended or PTNR for partner. Depending on your plan with your host network, this is usually free.