It's important to recall that when Canada made its initial concessions under the Trans-Pacific Partnership, the United States was still part of it. The concessions that were made at the time were for an area that included the United States. When they withdrew, they demanded additional concessions just for them.
Of course, if the United States were to join the Comprehensive and Progressive Agreement for Trans-Pacific Partnership, it might have to come to an agreement with Australia or New Zealand on quota-sharing , to take on some of the quotas that would have been granted under the agreement, but there is no reason for any further concessions because the volumes granted had been conceded when the United States was in the partnership.