They're not at the negotiating table, but they are regularly consulted. Typically, sub-federal governments are not involved in trade negotiations anywhere around the world. There is one exception. During our trade negotiations with the European Union, the European Union asked that our provinces be brought to the table when we were negotiating in areas that had impacts on their jurisdiction. I believe the outcome we were able to reach reflects the fact that our provinces had that input in the crafting of the agreement.
On May 11th, 2015. See this statement in context.