But familiarity does not necessarily imply deep friendship. Intertwined though their economies are through the North American Free Trade Agreement, Mexico's hopes of forming part of something like the European Union are forlorn. Harper shuns trilateralism, and seems to care only about strengthening Canada's bilateral ties with Washington. And since 2001, the United States has been less interested in integration than in border security.
This year the leaders will talk about their economies' problems. Both Canada and Mexico abhor the "Buy American" clause in Obama's stimulus package. Calderón will press Obama to fulfil his promise earlier this year to restore a pilot scheme allowing Mexican truckers to travel north of the border.
Talk of setting a common position on climate change looks ambitious. The big success has been co-operation on public health. Thanks in part to a committee established at a previous summit, Mexican authorities worked closely with both U.S. and Canadian laboratories to tackle swine flu. Diplomats hope to reinforce this co-operation before the bug's expected resurgence in the autumn.
The meeting may be dominated by the issue of security. On a visit to Mexico in April, Obama accepted that confronting violent drug traffickers was a "shared responsibility." Since then U.S. officials have made bigger efforts to halt the southward flow of guns and money to the drug industry. So far this year they have seized $25.5 million in cash destined for Mexico, almost five times as much as in the same period of 2008. All trains at main border crossings are now inspected. Mexican officials say that intelligence sharing has improved. Friction remains. The release of $100 million in anti-drug aid to Mexico has been slowed by concerns about abuses by the army. But Harper may offer Mexico help in training its police forces.
Calderón is likely to berate Harper over Canada's sudden decision last month to require Mexicans to obtain visas before travelling to the country. This followed a big increase in the number of Mexicans turning up in Canada and claiming to be refugees. Clamping down on abuses in the immigration system is popular in Canada. But in this case it does nothing to boost economic ties and tourism between supposed partners.