Does Fizz plan to expand their network coast to coast in a near future?

I think it depends on Videotron’s plan. However you can check the dynamic coverage area to see whether new areas are being included:
https://fizz.ca/en/faq/subscription-area-and-coverage-area

Loup-Philippe, they probably can given that Videotron is coast to coast. It would depend on if they think it's a good business decision to do so based on who their competition winner be in other areas.