Technically, the NAFTA would remain in force as between the United States and Canada. This is what we think, but it's not entirely certain.
What would happen in that event is that the United States could decide to withdraw from the NAFTA. We know that the President has condemned the NAFTA as one of the worst agreements the United States has ever entered into. If Canada could not or refused to ratify the new agreement, bringing the the NAFTA back into force, would the United States maintain the NAFTA? I think that is in some doubt.
Whatever happens, there would be tremendous uncertainty. How you would reconcile the NAFTA, if it did continue, with the CUSMA or the USMCA, as it would be, would be highly problematic.