Prime Minister Stephen Harper said Tuesday that re-opening NAFTA would actually help the Canadian economy, because Canada is the biggest supplier of oil and gas to the United States.

"That is of critical importance to the future of the United States, and if we had to look at this kind of option I think that would put us in an even stronger position than we were 20 years ago," Harper said at the North American Leaders' Summit in New Orleans.

But he added that his preference "is not to renegotiate what we discussed in the past, and to talk about the future."

The North American Free Trade Agreement helps generate roughly $1 trillion in annual trade between Canada, the United States and Mexico.

Harper, at a joint press conference with U.S. President George Bush and Mexican President Felipe Calderon, said that NAFTA was a major issue at the summit.

"We discussed the importance of co-operation on security and trade and the benefits that NAFTA has produced for each of our three countries over the last 14 years," he told reporters.

"We agreed that continuing to improve and expand trade is the key to greater prosperity for our peoples and we are putting special emphasis on the Detroit-Windsor crossing."

Both Bush and Calderon also expressed a preference for not re-negotiating NAFTA.

Bush also addressed criticisms of NAFTA from Democratic presidential candidates Hillary Clinton and Barack Obama.

"Now is not the time to renegotiate NAFTA or walk away from NAFTA," he said.

Harper said "North American co-operation" is the "best option to create jobs and to compete effectively with emerging trading blocks elsewhere in the world."

However, he said he was concerned about the "thickening of the Canada-U.S. border" that hinders the movement of people and goods.

The North American Leaders' Summit is the fourth such meeting between North America's most prominent leaders.

The Security and Prosperity Partnership between the three countries was specifically designed to increase efficiencies within NAFTA.