Republican presidential candidate John McCain (web|news|bio) will give a speech next week in Canada about free trade, which could pull the country into the presidential debate once again. His presence and subject matter is bound to revive the controversy over NAFTA that embarrassed his Democratic rival, Barack Obama (web|news|bio) , earlier this year. McCain, an avowed free-trader, is to speak to the Economic Club of Canada in Ottawa on June 20, the club announced Wednesday.

Obama's sincerity was called into question last March after the leak of a Canadian diplomatic memo, which summarized a meeting between senior Obama adviser Austan Goulsbee and Georges Rioux, Canada's consul general in Chicago.

According to the memo obtained by The Associated Press, Goulsbee suggested that Canada shouldn't take seriously Obama's campaign rhetoric about renegotiating the North American Free Trade Agreement. Goulsbee insisted that his words had been misrepresented but the leak is widely thought to have contributed to Obama's defeat in the Democratic primary in Ohio, where NAFTA is unpopular.

Canadian opposition member of Parliament Bob Rae said McCain's speech suggests Canadian Prime Minister Stephen Harper's government is playing favorites in the U.S. presidential contest.

"It's hard not to wonder what this is all about given the previous history of this story and I'm sure he would not have come unless he was told by the government of the day that it was a good idea," Rae said. "It does put Canada in the middle of the campaign."