Joseph Decunha said he had driven to a border crossing between Champlain, New York and St. Bernard de Lacolle, Quebec, with his partner and friend who are both Americans, on Thursday night.
"Upon arrival, we told the border patrol officer we're heading down to DC and will be attending the Women's March and will be in DC the day of the inauguration," he told CNN.
The group was asked to go through a secondary inspection.
At the second border inspection, they were asked if they were pro- or anti-Trump, Decunha said.
"We were honest and said we were anti-Trump and at that point, he engaged me directly in conversation because I assumed I was the only Canadian," he said.
Decunha elaborated as to why he didn't support Trump and talked about the Affordable Care Act and other policies he disagreed with.
The line of questioning veered towards whether they had been to the Middle East and if they believe in violence. Decunha said he thought the officer was trying to figure out if they were radicalized.
Decunha was told that he was denied entry to the US.
The officer used the term "silent disruption" as the reason and Decunha said he "kept dropping it as though it was a verifiable law regulation to not let me in the country."
Angered by the denial, Decunha's partner, who is American, began arguing with the officer. During that exchange, the border patrol officer said Decunha couldn't come into the country under the purpose of tourism.
Decunha said he was told, "If you would've said you were pro-Trump, that would've put you in the tourist bin and would have been allowed entry."
His two American travel companions were allowed entry, but Decunha said he was denied. He was fingerprinted and photographed before he was allowed to return home.
CNN contacted the US Border Patrol and Customs, but has not received a response.
Another Canadian told CNN a similar story, also at a border crossing in Quebec.
Sasha Dyck said he was part of a group comprised of six Canadians and two French nationals who organized a trip to Washington for the Women's March.
They arrived at the border on Thursday and when Dyck mentioned the march, the whole group was pulled over for inspection.
They had to submit their phones and passports, he said. Then, their fingerprints and photographs were taken.
The border patrol guard was "quite curt," said Dyck, a research nurse at a Montreal children's hospital.
They got their items back and Dyck said he was told: "If you're trying to re-enter this weekend, you'll be arrested."
Unable to enter the US, Dyck ended up going to a woman's march in Montreal instead.
"It was just a surprise. I usually think of the [US] as open to diversity of ideas and opinions, but not this weekend," he said.