MONTEBELLO, Quebec — President Bush's summit with the leaders of Canada and Mexico is likely to produce additional assurances of what unites them — and clear signs of what doesn't.

Bush came to this resort town on the Ottawa River to strengthen his ties with Canadian Prime Minister Stephen Harper and Mexican President Felipe Calderon. They were poised to announce at least one wrinkle, an effort to clarify border security plans in emergencies.

Yet for all the gestures of unity, there were differences that were handled much more gingerly, spanning from Arctic waterways to passport policies to the war in Afghanistan.

Overshadowing the two-day event was the menacing Hurricane Dean — to the point that the schedule was rearranged to accommodate Calderon. He will attend every event today but will leave Canada earlier than planned to head home, where Mexico is bracing for the storm.

Security and trade issues dominated talks among the North American leaders. Their goal is to make their borders safer without impeding their trade-and-tourism relationship.

Yet even their security partnership has stirred fears in Canada and the U.S. that more North American integration will derail national sovereignty. About 2,000 demonstrators descended on the Montebello in protest; police used tear gas to push back several dozen.

Overall, the leaders stressed their common missions. The three men enjoy good relations. There was much talk of listening, understanding, and disagreeing politely.

A Canadian official said Harper plainly told Bush what he's said publicly — that Canada's mission in Afghanistan will not be extended beyond 2009 without a consensus in Parliament. Canada has 2,500 troops in Afghanistan, a commitment important to Bush.

Dan Fisk, a White House National Security Council official who briefed reporters, said Bush now has "a better understanding" of the dynamics Harper faces in Canada.

Harper also used the meeting to assert his nation's claim to the Northwest Passage through the Arctic. The United States says the passage is part of international waters.