Both sides were trying to hold their ground at the heavily-fortified resort for the two-day summit involving Prime Minister Stephen Harper, Mexican President Felipe Calderon and U.S. President George W. Bush. The three leaders are meeting as part of the Security and Prosperity Partnership — an initiative aimed at deepening the integration of Canada, Mexico and the United States.

The riot squad had earlier prevented Council of Canadians chairwoman Maude Barlow from delivering a 10,000-signature petition to the gate. Council officials claimed this violated a prior arrangement with summit organizers.

Montebello's main roads were closed by police soon after most of the protesters — estimated at about 1,000 people — arrived at noon Monday.

Faced with police resistance, most front-line protesters opted for an impromptu sit-in. Others began dousing their bandannas with vinegar in anticipation of tear gas attacks.

The Council of Canadian and certain other groups pulled back from the front line about 300 metres, for fear of escalation of violence.

The American president arrived in the early afternoon and was first greeted at Ottawa International Airport by Gov. Gen. Michaelle Jean. Bush gave a quick wave to photographers as he descended the stairs of Air Force One to shake Jean's hand.

The president and Jean chatted amiably, smiling often at each other, as they walked to an airport lounge, where they met privately for about 15 minutes before Bush embarked on his helicopter for the ride to Montebello.

The Mexican president arrived at the resort around 4 p.m. ET.

Bush’s departure was slightly delayed when a Marine guard collapsed near one of Bush's helicopters while he met Jean inside the hangar. She required medical attention after apparently passing out from the heat on the tarmac.

The American president arrived at the historic Montebello resort at around 2:15 p.m. ET and mingled with the crowd of hotel employees who were outside to greet him. He was then driven around the grounds by limousine and walked down a pathway to meet Harper.

“Hi Stephen,” he said as he approached the prime minister. The two men, dressed casually in shirts and jackets, were to have a bilateral meeting before the Mexican president was scheduled to join them later in the afternoon.

As Bush was walking towards him, Harper was asked by a reporter what he thought of the protesters. “I've heard it’s nothing. It's sad,” he said.

This is the third summit between the North American leaders and the agenda for this year's meeting includes border security, energy, the environment and food and product safety.

Hundreds of police officers are keeping a watchful eye on the protesters, who condemn the SPPas secretive and anti-democratic. They also worry about stronger ties between the North American countries.

Behind the security fence that was specially erected around the posh resort, RCMP officers were stationed about every 20 metres and hundreds more lined the road into the resort, along with officers from the Quebec police force. Police were also patrolling the adjacent Ottawa River by boat and on personal watercrafts.

On Sunday, a large warm-up demonstration was held in Ottawa where protesters marched through the streets, passing by the American and Mexican embassies before rallying on Parliament Hill. The crowd, under the watchful eyes of a large police contingent, was peaceful.

Residents and business owners in Montebello are hoping for the same tone over the next two days but have braced for the worst. Some businesses are closing until Wednesday and have boarded up their storefronts to try and protect against any vandalism.

A three-metre high fence surrounds Chateau Montebello, where the meetings will take place, and boat owners mooring at the small marina next to the resort are being told to move their vessels to make room for helicopters.

Hotel staff expect to go through police scanners before boarding special shuttles to work. Two protest zones have been set up outside the perimeter of the resort grounds to accommodate the demonstrators.

Calderon, who is keeping a close eye on Hurricane Dean which is set to pound his country in the next few days, will have his own meeting with Bush and then all “three amigos” will have dinner Monday evening.

The leaders will meet on Tuesday morning with the North American Competitiveness Council, a collection of 30 business leaders, 10 appointed by each country, who advise the leaders.

The Council was created in 2006 and is one of the only tangible results of the SPP process to date.

The group, whose Canadian executives include Dominic D'Alessandro of Manulife Financial, Paul Desmarais Jr. of Power Corporation, and Michael Sabia of Bell Canada, will present a progress report to the leaders.

It is the Council that is a main source of contention for critics of the SPP, who argue the North American governments are consulting only corporate leaders and ignoring labour leaders, human rights experts, environmentalists and even legislators.

“The problem with this process is that there has been no public consultation, and no parliamentary debate in any of our three countries,” says Meera Karunananthan, a spokeswoman for the Council of Canadians, one of many activist organizations planning to attend the protests in Montebello.

Liberal Leader Stephane Dion and New Democratic Party Leader Jack Layton have both been critical of the SPP and its degree of transparency.

With the backing of the Liberals and the Bloc, NDP trade critic Peter Julian successfully pushed for three days of committee hearings on the SPP this spring. But he says that's not nearly enough, given the vast scope of the deal. His party is calling for the SPP to be suspended until MPs and the public get a chance to examine it.

Dion is also planning a House of Commons resolution demanding more information.

The Liberal leader also charged last week that Harper is taking the SPP in a different direction than it was intended and the prime minister is embracing a “culture of secrecy.” He accused the government of being in “secret negotiations” with the U.S. to export water south of the border, a claim the government flatly denies.

The summit is not expected to produce any major deals or announcements.

Much of the discussion between the leaders will be bureaucratic in nature, said a government official last week. “A lot of it isn't very interesting,” the official said.Protesters went nose to nose with riot police outside the Chateau Montello’s main gate Monday afternoon, though more serious violence has so far been avoided.

Numerous scrums and pushing matches erupted between bandanna-clad demonstrators, linked by arm, and Sret du Qubec squads armed with batons, shields and gas masks.

Both sides were trying to hold their ground as North America’s leaders arrived at the heavily-fortified resort. The riot squad had earlier prevented Council of Canadians chairwoman Maude Barlow from delivering a 10,000-signature petition to the gate. Council officials claimed this violated a prior arrangement with summit organizers.

Montebello’s main roads were closed by police soon after the majority of protesters – estimated at about 1,000 people – arrived at noon Monday. After the petition, being transported on a trolley in three transparent boxes, was halted, a second group of riot police dramatically emerged from a forest pathway leading down to a crypt. They also fanned into the adjacent cemetery.

RCMP officers and dogs watched the tense situation from inside the temporary security fence erected around the hotel. Faced with police resistance, most front-line protesters opted for an impromptu sit-in.

Others began dousing their bandannas with vinegar in anticipation of tear gas attacks. The Council of Canadian and certain other groups pulled back from the front line about 300 metres, for fear of escalation of violence.