Yesterday, Canadian television reported that Obama advisors were telling Canada's ambassador in Washington not to take the candidate's NAFTA rhetoric too seriously. Now what really seems to have happened is that Austan Goolsbee tried to get someone from the Canadian consulate in Chicago to be a bit less worried about Obama. Whatever the details, this kind of ambiguous messaging is likely to recur time and again.
I recall being at a meeting in Cambridge, MA around the time of the 2004 Democratic Convention where John Kerry's top economic and foreign policy advisors were essentially promising a group of assembled ambassadors that all of his anti-trade rhetoric was just empty rhetoric. This seemed like a typically Kerryish thing to have happen, but it would serve Obama may to try to avoid the same kind of thing repeating.