Just across the Canadian border is Cornwall, a growing manufacturing city with a population of about 50,000. Those consumers once made regular trips to Massena and Malone to shop in American grocery stores, pick up Amazon packages that would ship only within the United States and eat the chicken wings at Trombino’s.

“I could get food for my kids that we didn’t have here,” said Alyssa Baird Payette , 36, a mother of two who lives in Cornwall. “The clothing stores there always had more options.”

The mall that now sits nearly empty had been constructed with Canadian shoppers in mind, said Jim Murphy , the executive director of the Business Development Corporation in Massena.

But as the value of the Canadian dollar began to fall in 2013, American goods became more expensive for Canadians, and Ms. Baird Payette — like many of her neighbors — visited the United States less frequently, she said.

Then stories began spreading in the past two years of Canadians who were stopped at the border for hours for seemingly innocuous reasons such as carrying produce or misstating their reason for visiting. Many stopped coming altogether.

“I think I’ve gone once in the last year. It’s just not worth it anymore,” said Katie Digirolomo , 35, who said her husband had been repeatedly stopped when he tried to go to a casino across the border.