So how much provincial power scope creep will be allowed before Carney steps in and does something? (Or the next PM, but Carney in particular seems well placed to do so gracefully)

In theory, no. They seem to be testing that.

Two are needed, two are safe seats, the Liberals have a double digit poll lead.

This and how hard it would be to ever amend the constitution (y’know, to move away from FPTP, for example) are the biggest problems for Canadian democracy going forwards.

It won’t sink us in the next 10 years, but past that who knows. History has a way of turning heroes into villains, and vice-verse.