In the original agreement, the United States and Japan negotiated a bilateral annex to the agreement that addressed some of these non-tariff barriers faced by North American auto producers. After that negotiation, Canada negotiated a parallel agreement with Japan. Essentially after the United States left, the agreement was no longer in effect, and that was the purpose of the side letter. It deals with the same issues that were negotiated in the original agreement between Canada and Japan.
The main issues addressed in the side letter are that Japan has agreed to streamline certain testing procedures that provide national treatment for financial incentives under Japan's preferential handling program; Japan will now recognize the United States federal motor vehicle safety standards, including with respect to cars made in Canada; and we've agreed to work together with Japan to promote greater international harmonization of requirements through other multilateral fora. These, along with the noise and exhaust emission certification procedures, for which Canadian-made vehicles will be treated as Japanese vehicles, are all enforceable by a binding dispute settlement.