The demonstrators had gathered near the site of ongoing National Energy Board hearings into a plan by Enbridge Inc. (TSX:ENB), a proposal that would reverse the flow of a pipeline to send Alberta oil through southern Ontario and Quebec.
Environmental groups, First Nations and residents who live along the pipeline's route say the project would put communities and water sources at risk.
For one protester from Nova Scotia, Thursday's demonstration was an opportunity to deliver a political message about Canada's oil industry — but her effort ended in tears.
Before the march, an optimistic Chelsea Fougere, who studied environmental sciences before recently moving to Montreal, said she hoped the protest would make politicians understand that citizens don't want the Enbridge project to move forward.
"I think it's really scary that the Government of Canada puts so much value on oil without understanding what they're doing to the environment," said Fougere, who held a sign that read: "Clean water & safe homes are far more valuable than oil."
"It's a very unstable game they're playing with our security, with our lives."
After the protest, however, Fougere could be seen fighting back tears, as she, and several fellow demonstrators, were surrounded by armoured police officers.
Montreal police have become increasingly aggressive in limiting protests since the rowdy student demonstrations of 2012 and they didn't let this one last long.
They declared the gathering illegal before people had begun to march and, after tolerating the walk for several blocks, they stepped in to stop it.
Helmeted officers knocked several protesters to the ground as they charged the group of demonstrators. A few marchers were cuffed and placed in police cruisers, while others were penned up in a kettle.
The city has a municipal bylaw that requires protesters to provide an itinerary in advance. The local police force began applying it at the height of nightly and frequently disruptive street demonstrations last year over tuition hikes.
Twenty-nine protesters were detained, and face fines, for violating that municipal bylaw, P-6. Three others were arrested and face possible criminal charges for assaulting police officers.
One McGill student, who took part in the march, said he knew several people who had been detained by police. He said officers didn't even let protesters walk on the street before they began making arrests on the sidewalks.
"They are trying to suppress the voice of the people who are trying to protest something that is pretty legitimate," said Nicolas, who did not want to give his last name.
The energy board hearings into the Enbridge project come at a time when Canada is struggling to find routes to deliver oilsands bitumen to foreign markets amid stiff resistance fuelled by safety and environmental concerns.
The Calgary-based company hopes to reverse the flow and increase the capacity of its existing Line 9, a pipeline that stretches from Sarnia, Ont., to Montreal.
Enbridge argues the project would provide refineries in Ontario and Quebec with a more secure oil supply at a lower price than the foreign product they currently buy. The reversal, the company says, would create jobs and boost provincial revenues.
Fougere said many young people from her Nova Scotia hometown have moved to the Alberta cities of Fort McMurray and Cold Lake to land oil-industry jobs.
She said she was also encouraged to go to Alberta in search of work, but instead decided to stay away and push for change.
She doesn't want the oilsands crude to flow east, either. Fougere called oil an old-fashioned business that needs to be replaced by new, cleaner technologies.
"As humans we need to progress, we need to move forward," she said before the march.
The National Energy Board hearings will be held in Toronto next week. The panel has three months to deliberate and is expected to reach a decision by early 2014.