Something has changed. Under the GPA, that is, the agreement under which the U.S. opened the markets in its states, Canada had no access to these markets because it had not established the same obligation. However, the other GPA parties did have access to the 37 markets. Therefore, the 37 markets were available to all the GPA parties, except for Canada. This is what has changed.
On March 11th, 2010. See this statement in context.