By Caren Bohan

OTTAWA, Aug 21 (Reuters) - President George W. Bush will try to assure leaders of Canada and Mexico on Tuesday that the United States wants to build closer ties with them, despite the distraction of wars in Iraq and Afghanistan.

But the Quebec summit between Bush, Canadian Prime Minister Stephen Harper and Mexican President Felipe Calderon risked being overshadowed by a monster hurricane threatening to wreak havoc on Mexico's Yucatan peninsula.

Not long after he arrived in Montebello, Quebec, for what has been dubbed the "Three Amigos summit," Calderon announced he was cutting his trip short to deal with a potential catastrophe from Hurricane Dean.

Dean killed at least 11 people as it blasted through the Caribbean islands. It strengthened into a monster Category 5 -- the strongest type of hurricane -- and was to reach Mexico's coast early on Tuesday.

Bush told Calderon the United States was willing to help after the storm. "We want to be in a position to help them as appropriate and as best we can should Dean hit any part of Mexico," said Dan Fisk, a White House specialist in Western hemisphere affairs.

Calderon canceled plans for a meeting with Harper as well as a business lunch in Toronto. The leaders were still due to hold a news conference around midday.

The summit at the chateau by the Ottawa River got under way amid demonstrations by protesters who shouted for Bush to go home and objected to the aim of boosting trade and working on a common approach against terrorism.

Critics expressed concern that broadening economic ties would erode national sovereignty and that closer cooperation on anti-terrorism could lead to human rights abuses.

DON'T APPEAR TOO CLOSE

But both Harper and Calderon are interested in furthering the trade relationship, although neither wants to appear too close to Bush, who is unpopular in both of their countries.

Bush came into office in 2001 pledging to focus on strengthening ties with Mexico but critics say he has neglected the concerns of his North American neighbors in the aftermath of the Sept. 11 attacks.

Mexico is frustrated by increasingly tough U.S. border policies and by the collapse in Congress of a push to overhaul U.S. immigration laws.

Canada is irked that anti-terrorism measures have hampered the flow of goods and services across the border.

Harper discussed Canada's concerns about Russia's symbolic laying of claim to the North Pole, where it placed a flag on the seabed. Canada claims it has sovereignty over the Northwest Passage of the Arctic, but the United States views it as an international strait.

"I think it's fair to say the president came away with a far better understanding of Canada's position," Fisk said. "However, I will note that from the U.S. position we continue to believe that the Northwest Passage is an international waterway, that there is international navigational rights through the Northwest Passage," he said.

"It's a very safe issue for Harper to bring up because it allows him to sound a nationalist theme," said Stephen Clarkson, a professor of international economy at the University of Toronto.

"It also allows him to have a little bit of disagreement with the United States," said Clarkson, noting that opposition politicians have accused Harper of being a Bush protege.

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