The car side agreement with Canada will probably be similar to the side agreement with Mexico:
“Mexico and the United States have agreed to a side letter to the new trade agreement announced Monday that will protect some Mexican auto exports against possible “national security” tariffs, Economy Secretary Ildefonso Guajardo said yesterday.
Under the arrangement, which Guajardo described as “insurance for Mexico,” if the United States government applies Section 232 tariffs to auto imports — as it did to steel and aluminum earlier this year — Mexico would still have duty-free access to the U.S. market for vehicles that comply with the new rules of origin, but only up to a certain limit.
Guajardo explained that the cap was set 40% above the 1.7 million cars Mexico currently exports annually to the United States, which he said gave Mexico’s auto industry scope to grow before facing the potential national security tariffs.”
source: https://mexiconewsdaily.com/news/some-exports-protected-against-national-security-tariffs/
The side agreements are important in the case of national security tariffs against car imports from Japan and Europe.
This will prevent those countries from producing in Mexico/Canada and shipping products to the USA to avoid national security tariffs.