Maybe I can answer.
I will give you some context. I think it would be useful.
Canada is a signatory to approximately 120 international tax treaties and information exchange agreements. Close to a third of those agreements contain clauses that, in certain situations, may allow the federal competent authority—the Canada Revenue Agency, in this case—to exchange some information with a subnational authority, to the extent that determination of a basic change at the federal level has direct implications at the provincial level. Exceptions in some of the existing treaties permit such an exchange.
These exceptions were created and agreed to by the various parties, and were based on the way the current federal-provincial tax system is set up. In the event of a decentralization of the federal system that would give administrative power to one province, it's not clear whether the rules of the treaties would be interpreted in the same way. It could require further negotiations.
As I said before, this applies to about a third of our agreements. The other agreements contain no similar exceptions.