Again, this is not part of the intergovernmental agreement, but it would be a question as to the application of the Canada-U.S. treaties' exchange of information provisions generally. Under those provisions, it's possible for the U.S. to request information that's relevant to the administration of its tax system. If it's relevant to the U.S. tax system, the request could be made.
On May 6th, 2014. See this statement in context.