This way, any province that wants out of diry and cultural and other protectonism could finally bow out and trade with the world. If another province wants to raise tariffs against it, so be it. It could always trade with the other provinces, the US, and the rest of the world instead. Let the protectonists protect and the traders trade.
On that note, transfer control over packaging and labelling, phytosanitary, banking, and other economic matters to the provinces too.