Canada

The Notwithstanding Clause doesn't contravene Treaty Rights or Section 35 of the Charter of Rights and Freedoms:

Section 35 of the Constitution Act, 1982, which recognizes Aboriginal and treaty rights, is generally considered immune to the Charter's notwithstanding clause (Section 33) because Section 35 falls outside the Charter itself, existing in Part II of the Constitution, meaning legislatures can't override these Indigenous rights with the clause

(AI summary, but accurate to my understanding)

So the Notwithstanding Clause is irrelevant, in terms of the government's obligations to meet Treaty Rights. Even moreso, the Supreme Court of Canada has ruled that Treaty Rights supercede the Constitution since (roughly) they predate the Constitution.

I'm not a lawyer, but I assume that Treaty Rights would make separation legally complicated, at best, if not practically impossible under the current legal system.