MONTEBELLO, Canada - 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.