There are many practical and political challenges to be overcome on the way. But if we could reach agreement on deepening and/or broadening NAFTA, it would be extremely valuable. It would spread the benefits of competition across more industries, reduce uncertainty stemming from unilateral trade actions, and greatly reduce non-tariff barriers (which are often even greater impediments to trade than tariffs).
And if we could agree on common external trade rules and tariffs, rules of origin could be eliminated and matters at the border would be enormously simplified.