"So far from God, so close to the United States."

That lament by a former Mexican president, Porfirio Diaz, seemed to sum up the attitude of many Canadians during the recent election campaign, which featured a national debate of sorts on Canadian anxieties about the country next door.Americans don't often think about the impact their country has across its northern and southern borders, but both the Canadian elections and the inauguration of a new Mexican president next week have been calling attention to the advantages and adversities of geographical intimacy with the United States.

Canadian Prime Minister Brian Mulroney was on the defensive during much of the campaign, fending off critics who suggested that the U.S.-Canada free-trade agreement would leave Canada as little more than an appendage of the United States, further robbing his countrymen of a national identity.

In the end, though, a plurality of Canadians felt that the agreement and its promise of economic boom was too good an opportunity to pass up, and Mulroney and his Progressive Conservatives were returned to office.

As for Mexico, some argue that having the United States as a neighbor is an unmitigated blessing. Proximity enables Mexico to send at least part of its surplus population to the United States and more than $13 billion worth of exports in most years.

But the United States is, of course, the country which seized half of Mexico's territory a century and a half ago and, as in Canada, U.S. cultural and economic penetration of Mexico sometimes creates psychic torment among Mexicans.

Mexico, says Assistant Secretary of State Elliott Abrams, has a "fear of being swamped culturally or economically. Whether you consider it real or not, it's there. And it's a political factor."

Former Mexican Finance Minister Jesus Silva Herzog, at a news conference Wednesday, reinforced this thesis when he said he doubted that Mexico would follow Canada's path and negotiate a trade agreement with the United States.

"We like the English language but only as a second one," Silva said.

The notion that Mexico likes to assert its independence by staking out anti-American positions is espoused by former Secretary of State Henry A. Kissinger, who once said that Mexico is institutionally incapable of embracing any foreign policy position to the right of the United States.

Thus, Mexico maintains close ties with Cuba and Nicaragua, the principal hemispheric adversaries of the Reagan administration.

The objections of many Canadians to the United States go beyond the fear of creeping assimilation from the south. They look on the United States as a far less humane society and that the free trade agreement could lead to the dismantling of government social programs and a large dispossessed underclass similar to that in the United States.

"We're not anti-American," says Rick Salutin, a Toronto playwright who campaigned against the trade agreement. "We just don't want to be American." Salutin obviously does not speak for the many other Canadians, including some of the country's most talented offspring, who admire American dynamism and have packed up and headed south.