Canada's government is being dragged deeper into a re-invigorated U.S. debate over NAFTA, with Democratic rivals Barack Obama and Hillary Clinton saying they might opt out of the deal.

"You've got a right-wing government in Canada that is trying to help the Republicans and is out there actively interfering in this campaign," Democratic strategist Bob Shrum said Sunday on NBC's Meet the Press.

In an interview with CTV News, Liberal MP Mark Holland was skeptical of improper interference by the Conservatives.

"Right at this point, I don't see that," he said. "What I do see is NAFTA being used as a political football -- a lot of games being played with something very serious."

The debate started when both Clinton and Obama took aim at the North American Free Trade Agreement in a Democratic presidential candidates' debate.

"I'm confident that as president, when I say we will opt out unless we renegotiate, we will be able to renegotiate," said Clinton during Thursday's debate.

When asked if she felt the agreement was a mistake, she said, "NAFTA was a mistake to the extent that it did not deliver on what we hoped it would."

Obama sided with Clinton, saying that he would use the agreement's six-month cancellation clause as a leveraging tool to renegotiate it.

"I think, actually, Senator Clinton's answer on this one is right," he said. "I think we should use the hammer of a potential opt out as leverage to ensure that we actually get labour and environmental standards that are enforced."

But sources told CTV News that both camps called Canadian diplomats in the U.S. to say the candidates didn't really mean it. They were just looking for votes in Ohio, where the trade deal is blamed for massive job losses.

"I've learned to take with a grain of salt what opposition politicians say about trade deals during election campaigns," Prime Minister Harper said.

Echoing the sentiment was Peter Beinart, editor-at-large of The New Republic, on CTV's Question Period on Sunday.

"I think this is really a kabuki dance done in preparation for (the primary in) Ohio, which was a state that's been hit very, very hard by layoffs," he said.

Beinart said that nationalism is a powerful force during a presidential campaign, but the realities of governing would prevent NAFTA from being overturned.

"Think of the consequences for America's relationship with Mexico and Canada if the United States were to somehow pull out of NAFTA. I think it's virtually inconceivable," he said.

The Canadian embassy denied it was ever called by either camp, but Republicans are still accusing Clinton and Obama of misleading voters.

"I'm going to put my faith in what Count Bismarck said, which is, 'The greatest lies are told before the marriage, after the hunt and during the election,'" Republican strategist Mike Murphy said on Meet the Press.

With a story by CTV's Roger Smith