You certainly raise an interesting point.
It's always important to be clear when discussing the right to self-determination. On one hand is the right to external self-determination, which is basically akin to secession. On the other is the right to internal self-determination, the exercise of governance, say, by a people in control of a federated state.
In this case, we are talking about internal self-determination. I agree that having a Canadian constitution that has been adopted by the other provinces and by the federal government, without Quebec's consent, is a violation of the principle underlying the right to internal self-determination. That's problematic for federalists and sovereignists alike, especially because the Constitution results in a loss of protection of the French language in Quebec. That's where the use of parliamentary sovereignty, in other words, the notwithstanding clause, comes into play.
Since Quebec's Charter of the French Language was passed in 1977, particularly after the Canadian Charter of Rights and Freedoms was passed in 1982, judges have had considerable influence over Quebec's language policy. That has systematically led to declining protection for the French language in Quebec, and census data now illustrate the impact of that decline.
Under the current model, authority is delegated, and the final say often goes to judges, not lawmakers. Judges, especially those who sit on the Supreme Court, wield tremendous power. If that model worked well, striking the right balance between the protection of francophones' rights, the protection of anglophones' rights, the protection of individual rights and the protection of French as a common good, the census data would show as much. We would know it. That model isn't working, though, so it's time for a rethink. Quebec lawmakers should have more power, and judges should have a little less because the system isn't working.
In theory, a neutral arbitrator to protect fundamental rights is a good idea. In theory, it's great. When that idea is put into practice, however, the outcome is revealed by the latest census data, a disastrous situation for French.