Nothing works in parts of Northern Ontario unless you have TBayTel service.
CRTC allowed them to have a total monopoly on cell service in northern Ontario because of the initial start up cost of installing sufficient towers to provide service even in the 'larger' population areas.
Keep in mind that there are great expanses of Canada that still have no cell phone service whatsoever. Even on the major highways such as the TransCanada I can count on being out of range of cell service for miles at a time.
Most businesses that have 'remote employees' have to depend on satellite phone service to provide their employees with communication services.
Depending on where you're planning on travelling you may want to rent a satellite phone. If you're staying in major urban areas mostly then you may want to also use free wifi to supplement your own cells service- all Tim Hortons, Starbucks, McD, etc. etc. will have it.