Smaller pro leagues (MLS, WNBA, CFL) tend to do well in cities with less competition, and Quebec is in the sweet spot in that regard. It's reasonably big but with almost no pro sports to speak of.
I'm in Winnipeg and while people tend to think of us as a one-team town with the Jets, the reality is that the Blue Bombers are a major deal, they draw big crowds and bring in over $50 million a year. Add to that the AHL, minor league baseball, a popular CEBL basketball team and a CPL soccer team (admittedly on life support, but still). It's a lot for a city of this size.
By contrast Quebec has pretty well the same population, but has only the Remparts (junior hockey), a minor league baseball club (the only actual pro team) and a well supported university football team. That's not much. And they have a fabulous arena too. So it could be a really good niche market for the PWHL, there's a lot of discretionary sports spending that a PWHL team could tap into.