Canada as a whole has done a terrible job of encouraging immigrant groups to play hockey.
Elementary schools here are maybe 25% South Asian and 40-50% non white. But youth hockey is still 90%+ white.
There's been lots of growth of hockey in Indigenous communities in the last 20 years though.
You make a good point and I agree to an extent, but I think it can easily devolve into an anti-immigration argument for an easy shifting of blame. I think the causes are much more multi-faceted and are more related to cultural shifts (which may have immigration as a catalyst, but not the sole one).
For background, I am an immigrant. My parents were not from Europe or any other hockey-exposed country. My parents were from Asia. We came here in the 1970s.
Back then, immigrants as a whole were much more immersive culturally into their new Canadian environment. We adopted the language and the cultural nuances of life in Canadian society. Many immigrants watched hockey on TV as the parents' would have been in the workplace with other adults who watched hockey and whose kids played hockey. As such, many of us played hockey at a rec level, house league level, and perhaps even higher. We collected hockey cards, had opportunities to go to games (much more affordable back then), and it helped that we had decent teams in the recent memory (at the time) and emerging great teams coming up. Immigrants by and large embraced the Canadian life, which included hockey as an integral part of it.
Look at the cultural shift nowadays. Society is much more individually focused, rather than collectively (this is bad, in my opinion). Similarly, people who immigrate here are told they can pretty much bring their identity with them, along with all their previous practices and interests, and there is little to no cultural mandate to integrate into a new Canadian identity. As such, we in Canada are now comprised of much more splintered communities than previously. As a visible minority immigrant, I can say with confidence that this shift has not been conducive to promoting a singular Canadian culture and more importantly, embracing our rich history. Rather, it's you do what you want, I do what I want,
So unlike when I was a kid where hockey was part of the cultural landscape, it isn't necessarily so anymore due to the pluralistic nature of our society from a social and political perspective. That does have demographic playing a part, but it is not the only part. People are having less kids and having them older. My brother just had a baby at 47 (well, his wife did, not him). This was rare when I was a kid. The implications of this is, my brother will be too old and tired to drive my nephew (who is now 4) to any hockey practices. Add to that all the cost and time investment requirements and it is a recipe for a challenging landscape for hockey to flourish.
What Quebec may be experiencing is symptomatic of the trends in other parts of the country.