JUSTIN TRUDEAU gave the first of his Canada Day speeches on July 1st from the steps of a food-processing plant in Leamington, Ontario, the country’s tomato capital. By Canadian standards, it was a belligerent act. H.J. Heinz, an American company, moved its ketchup production to the United States in 2014, threatening to shut the factory, which employed 740 people. The plant is still in business under Canadian ownership (but with around 200 fewer workers). Mr Trudeau, the prime minister, came to exact revenge. Ketchup is among the C$16.6bn ($12.6bn) worth of American goods that are subject to tariffs imposed by Canada to retaliate against American levies on its steel and aluminium. The tariffs, including the 10% charge on ketchup, took effect on Canada Day.

The threatened plant closure made Heinz ketchup a target of consumers even before the trade spat. The Canadian market share of French’s ketchup, made with domestic tomatoes and processed in Canada, more than doubled. But now that the anger is directed at the United States, rather than at one firm, consumers are having to make tricky choices. “My visits to the grocery store are becoming more and more complicated and time-consuming, as I have to read every label,” tweeted a shopper under the hashtag #BuyCanadian.

French’s, for example, is owned by an American firm (McCormick & Co). Primo, however, is all-Canadian, according to a chart headed: “How Canadian is your ketchup?” Online guides on how to “shop like a patriot” suggest Royale toilet paper in place of Charmin, chocolatey Smarties instead of fruit-flavoured Skittles and Minute Maid orange juice, which is packed in Canada, instead of Tropicana from Florida. Some brands are less Canadian than they seem. Canada Dry is owned by Dr Pepper/Seven-Up of the United States but bottled in Canada, and Molson Canadian is owned by Molson Coors (but brewed with “Canadian water” in Montreal). It is easier to be picky about fresh produce, because its country of origin is clearly labelled.

Canadians buy more American foods than any other country, so the weaponising of shopping carts could affect the American economy (albeit not much). Canadian tourists, who made 42m visits to the United States last year, could deliver a slightly bigger blow. In 2018 they spent nearly $20bn. Steve Paikin, a television host, told his fellow Canadians to holiday elsewhere. “America, you just don’t deserve our money,” he wrote on his blog.

So far, the data do not show that trade is suffering. Imports from the United States rose 4.7% between April 2017 and April this year, the latest month for which figures are available. If they fall, one cause might be the depreciation of the Canadian dollar, whose value has dropped from 80 cents in April to 76 cents, partly because of the trade war. That may curb imports more than targeted tariffs do. The best test of Canadian feelings may come in winter, when hundreds of thousands of “snowbirds” flock to holiday homes in the southern United States. Will they brave Canada’s harsh weather or fly south, bringing bottles of Primo with them?