The U.S. president dismissed Canadian claims to the Arctic waterway at the closing news conference Tuesday of the two-day North American Leaders' Summit.

It was the one discordant note on a day characterized by back-slapping camaraderie and agreement to hammer out a series of protocols on trade, security and the environment.

Bush lauded Canada's efforts in Afghanistan and the leaders agreed to develop a crisis plan for North American borders, better safety screening for foreign food and goods, and harmonized fuel-efficiency standards.

But that spirit of co-operation came to a screeching halt over recent moves by Canada to bolster its ownership claim of the frigid northern waters.

"There are differences on the Northwest Passage," Bush said. "We believe it's an international passageway."

He quickly added that the U.S. does not question Canadian sovereignty over its Arctic islands, and he saluted Prime Minister Stephen Harper for his plan to build a military port and training centre there.

Harper said Canada will continue to strengthen its sovereignty in the Arctic and the two countries will be able to manage their differences.

Harper, Bush and Mexican President Felipe Calderon - who left promptly to deal with the aftermath of Hurricane Dean - wrapped up their summit with an agreement to work on stopping the import of unsafe food and goods.

The move follows a spate of safety scares linked to the "Made in China" label worldwide. Unsafe food additives, toothpaste and toys from China have all been in the international spotlight in recent months.

While there were few details, the leaders also agreed to:

-Set up a new emergency plan for their borders so that, in the event of a crisis, there would not be another crippling shutdown like there was after 9-11.

-Co-operate on fuel-efficiency standards for automobiles.

Harper used the news conference to mock critics of the Security and Prosperity Partnership (SPP), which is aimed at increasing co-operation on issues such as trade and security.

He scoffed at claims that the leaders are holding secret talks on issues such as bulk water exports and a NAFTA superhighway.

"A couple of my opposition leaders have speculated on massive water diversions and superhighways to the continent - maybe interplanetary, I'm not sure, as well," he said.

Harper added jokingly that one of the closed-door discussions involved establishing an international standard for the content of jellybeans, and ridiculed the idea that such a move would imperil national sovereignty.

He said it's simply a meeting of the three leaders to improve relations and streamline trade.

The Liberals accused Harper of failing Canadians at the summit.

"Mr. Harper did not commit to anything concrete as a result of his meetings. All Canadians got was a vague update on previous initiatives established at earlier SPP meetings," said Liberal Leader Stephane Dion.

Dion immediately announced that he will table a resolution when Parliament resumes to ensure full scrutiny of the SPP.

"It is clear that Prime Minister Harper has ignored the issues that are of utmost importance to Canadians when he had an important opportunity to raise them during his meetings in Montebello.

"Mr. Harper has dismissed critics of the secrecy of the SPP process, refusing to offer any substantive response to criticism from the business community, GOs and the Opposition that the secrecy of the talks is unacceptable and erodes the public's trust that their governments are acting in their best interests."

Dion got some support from a surprising source - the Canadian American Business Council. A report by the council chided the leaders for not being more open about the SPP.

It noted that one of the chief criticisms is the "lack of transparency" in the way in which a 30-member committee of business leaders from the three countries makes recommendations to Harper, Bush and Calderon.

The group said the political leaders should embark on a public education campaign to explain the SPP.

It also said non-governmental organizations and so-called civil society groups - not just blue chip corporate CEOs - should be invited to participate in the SPP.

The council also fears Canadian-American relations have been hijacked by the U.S. Department of Homeland Security, with security concerns trumping efforts to enhance trade and economic prosperity.

The NDP accused Harper of trying to minimize the significance of the SPP negotiations, calling his mocking tone "disingenuous and dishonest."

They countered by releasing a document obtained through Access to Information summarizing the results of a ministerial meeting on the cross-border initiative last February.

The document describes the SPP agenda as far-reaching, complex and "dense." And it notes that the big business committee advising the three governments has recommended "energy integration" as one of its priorities.

"We saw Stephen Harper today refer to this process as just something to do with jelly beans. It's a whole lot more," said NDP trade critic Peter Julian.

"It's food safety issues, it's air transportation, there are issues around water exports and, very clearly, issues around continued Canadian sovereignty in energy."

On Tuesday morning, the leaders met with top corporate executives to get their views on how to enhance trade and economic prosperity.

The meeting with the North American Competitiveness Council was a key complaint of critics who are upset that their elected leaders are only listening to the corporate elite and refusing to hear from social activists, environmentalists and others.

However, no protesters showed up Tuesday outside the sprawling Chateau Montebello resort where the leaders were meeting. It was a very different scene Monday, when police used tear gas and pepper spray to push back hundreds of protesters.

Harper met with Bush on Monday and the pair discussed border issues, trade, the war in Afghanistan, and Canada's sovereignty over the Arctic, officials said. Harper explained that he would need parliamentary approval to extend Canada's military mission in Afghanistan beyond February 2009.

At the closing news conference, Bush made an impassioned defence of Canada's role in the war-torn country.

He said he recognized that Parliament would make the right decision for Canadians - and for the people of Afghanistan. But he made his own preference clear in a lengthy, spirited monologue that extolled Canada's mission in Afghanistan as a historic and noble one.

"I think it's the calling of the 21st century. I think it's the calling of history," Bush said.

"And I appreciate the strong commitment that this government and the Canadian people have made. To be writing the first chapter of what will be laying the foundation of peace throughout the 21st century."

Officials said Harper told Bush during their meeting Monday that he regretted the U.S. withdrawal from talks to establish border pre-clearance rules that would speed up traffic at land borders, and added that he hoped to relaunch them.

Despite the jostling, tear gas and pepper spray from Monday's protests, it has been a far cry from previous meetings - such as the G-8, APEC and the Summit of the Americas - when thousands of people turned out and demonstrations turned violent.

There are seemingly as many causes as protesters, who condemn the secrecy of the SPP, North American integration, the wars in Iraq and Afghanistan, the leaders' performance on the environment, the plight of aboriginals, and human-rights abuses committed in the war on terror.