Theoretically, there’s nothing stopping any new country from joining getting a carve-out. You just need everyone to agree to it. And tbh, getting them to agree to let Canada continue using the Canadian Dollar is probably a much smaller ask than getting them to let a North American country into the European Union.
UK did exactly that. They never swapped their pound with euro. I’m all for it!
They were a founding member and got a special carve-out.
Theoretically, there’s nothing stopping any new country from joining getting a carve-out. You just need everyone to agree to it. And tbh, getting them to agree to let Canada continue using the Canadian Dollar is probably a much smaller ask than getting them to let a North American country into the European Union.