Cancun, Mexico ? President Bush, closing a three-nation summit Friday, defended requiring secure documents from border-crossing Canadians and pushed Mexico to prevent more of its people from illegally entering America.

Despite obvious divisions, Bush, Mexican President Vicente Fox and Canadian Prime Minister Stephen Harper emphasized North American unity and the productivity of their two days of meetings in this sunny spring-break area along Mexico’s Mayan Riviera.

The men emerged from joint sessions to laud the increased trade brought about by the 12-year-old tariff-reducing North American Free Trade Agreement.

The leaders said they intend to build on that progress – Canada and Mexico are the U.S.’s largest trading partners – to make their continent more competitive globally. And they pledged cooperation on new energy sources and bird-flu preparations.

“This is probably one of the most productive meetings we’ve had,” Bush gushed to Fox, the meeting host and a friend dating to before both assumed their nations’ presidencies. Fox said, “We have made a very good use of time.” And Harper announced a third annual trilateral meeting for next year in Canada – again framed around the Security and Prosperity Partnership the three nations formed a year ago.

But with disagreements still lingering – over everything from a Mexican murder investigation that has ensnared two Canadian mothers to a U.S.-Canada trade conflict over lumber and Mexico’s long-unrealized hope for a migration accord with the United States – there was little concrete to show for the leaders’ enthusiasm.

The long-standing dispute over U.S. tariffs on Canadian softwood lumber that is a major irritant in Ottawa didn’t even come up Friday, perhaps a sign of how stalemated the issue is.