According to the following report from Canada's CTV, last month a senior representative of the Barack Obama campaign called Canada's ambassador to the U.S. and informed him that, despite any anti-NAFTA statements Obama might make, it would all just be bluster and he wouldn't really mean it. Supposedly a Clinton representative made the same assurances to the Canadian government.

Both campaigns are denying it, but if they had actually done it it wouldn't be much of a surprise. No doubt foreign leaders are well aware that they have no intention of drastically modifying the trade deal and would at most seek to mollify those affected through various giveaways and the like.

Note also that Obama recently spoke in code, signalling his support for Bush's SPP (spp.gov), aka "NAFTA on steroids".

UPDATE: Taylor March says:

I called CTV to verify the story, especially given the Obama campaign's cries that it's "inaccurate." After asking Greg McIsaac of CTV if they were sticking by their story, he quickly called me back with verification. The facts of our story are accurate.

UPDATE 2: From CTV:

...the Obama camp did not respond to repeated questions from CTV on reports that a conversation on this matter was held between Obama's senior economic adviser -- Austan Goolsbee -- and the Canadian Consulate General in Chicago... Earlier Thursday, the Obama campaign insisted that no conversations have taken place with any of its senior ranks and representatives of the Canadian government on the NAFTA issue. On Thursday night, CTV spoke with Goolsbee, but he refused to say whether he had such a conversation with the Canadian government office in Chicago. He also said he has been told to direct any questions to the campaign headquarters.

More here.