Canada is already a federal structure with overlapping jurisdictions. Adding another layer to it complicates things, but doesn't fundamentally break anything. Treaties are just more laws in a constitution that is already a mix of Common Law, written law, (French) Civil Law, our history with the BNA act, and our recent constitutional patriation.

The USA has similar treaties, and the US Supreme Court has been flip-flopping trying to decide the limits of Oklahoma criminal authority in half the sate. It can be messy.

See https://en.wikipedia.org/wiki/McGirt_v._Oklahoma and https://en.wikipedia.org/wiki/Oklahoma_v._Castro-Huerta