HOLTVILLE, Calif. -- In this election year, in this place, in the rare event someone mentions Canada it's liable to be as a joke.

John Hernandez offers an example of the genre.

He greets a visitor to the southern tip of California and, upon learning he's Canadian, Hernandez cracks a quip about the border -- not the one nearby that everyone's talking about in the presidential election, but the other one, way up north.

"You gonna build a wall there too?" the retired state employee says upon encountering a Canadian reporter outside a cemetery in Holtville, Calif., a few kilometres from Mexico.

"No? Canada's not gonna have to build a wall and pay for it yourselves?"

He's being sarcastic.

He knows the answer to both questions is no. Like many here, he's noticed that only one of America's neighbours has become an issue in this election -- and it's not the one closest to the North Pole.

"People know the disparity," he said. "Mexicans are treated differently."

This tale of two disparately discussed neighbours has experienced its dramatic climax with Donald Trump flying into Mexico City on a public-relations mission Wednesday, followed by an evening speech where he doubled-down on his hardline approach of deporting millions, building a wall, and forcing Mexico to pay for it.

Trump delivered a one hour, 15-minute speech about border security without mentioning Canada.

It's the story of the campaign. Even when he raises an issue that seriously affects Canada, the northern neighbour's an incidental bystander. Like his threat to cancel a trade deal in the country that buys 76 per cent of Canada's exports.

In a major trade speech where he announced a renegotiation-or-cancellation policy on NAFTA, Trump referred to Mexican factories taking jobs; his campaign issued a statement railing against Mexico's allegedly unfair trade practices. But the northern amigo? Not a word about it -- negative or otherwise.

The dynamic played out at the Republican convention. The opening night's speeches featured anecdotes about Americans being killed by illegal immigrants from the south. In hallway interviews, delegates gushed about the northern neighbour.

They confessed they hadn't thought about it much during the election. Of the half-dozen or so people interviewed there, none were even aware the U.S. had a trade deal with Canada that predated NAFTA.

All agreed with bringing back the old Canada-U.S. accord if NAFTA got spiked.

A Texas convention-goer's eyebrows scrunched in surprise when a reporter asked about trade with Canada: "Why wouldn't we favour a trade deal with Canada? Canada's awesome," said Michele Montgomery. "I do lots of work with Canada... I like keeping my friends happy. And I have friends in Canada, so I'd like to see them happy."

One Republican deadpanned that he worried about the northern border. In the next split-second, he made clear he was joking: "No, we're not really worried about the Canadians," said Jeff Hommedahl, alternate delegate from Minnesota.

"Canadians are such nice people anyway. They're kind of like Minnesotans."

He said he supported trade with Canada because living standards are similar, as are salaries. He wouldn't expect American workers to lose jobs like they do because of commerce with poorer countries.

Loren Spivack said the purpose of border walls is stopping illegal migration: "The idea of a wall with Canada is kind of ridiculous," said Spivack, who displayed conservative-themed comic books outside the convention. "The border's 3,000 miles long -- and there's not much of an illegal immigration problem with Canada."

Closer to the Rio Grande, some people see a double-standard.

Enrique Morones is an advocate for southern migrants who drops water bottles in the desert to help them survive. It's true migration is a far bigger issue in the south but, he says, terrorism is also a concern in the north.

He's calling racism on it.

"Why does Canada not have a wall? We don't want them to have a wall. But why not? Because they have the same background (as the U.S.) -- Anglo-Protestant. If the people in Canada were brown or black, you bet there'd be a wall," said Morones, who leads the California-based group Border Angels.

"But it's like a cousin -- the first cousin of the United States. You're the same people. You're white. That's why there's no wall... It's a double-standard."

On rare occasions, U.S. media have questioned candidates about the differing rhetoric towards the two neighbours.

One politician got tangled in it.

NBC raised the issue with Scott Walker who replied that, yes, maybe a wall with Canada was worth considering. He was widely ridiculed; Trump brushed off the idea; and it was one of the final nails in the coffin of Walker's presidential campaign.

Canada's government is perfectly pleased to remain in the background of this story. Officials say there aren't any plans to follow Mexico's lead and invite the election candidates to Ottawa.

Meanwhile, the embassy in Washington is quietly engaged in behind-the-scenes outreach, and gathering research on how the players in the next White House and Congress might shape important issues.

"It doesn't matter who I meet with -- they're always friendly. It's amazing the number of times you see somebody and they say, 'I can't do anything to Canada because my wife's Canadian, or, 'My daughter goes to U of T,"' says Canada's ambassador, David MacNaughton.

"At that level there's an enormous amount of goodwill... That's all good. (But) when you get right down to the nitty-gritty, the issues that matter, they're tough.... What's in it for them?... 'What's it mean to my district, my state?"'

In the U.S. Congress, potential trade disputes loom over Canadian dairy imports and softwood-lumber exports.

North of the border, these pass for top-level bilateral irritants.