The protest, which has been held every March for the past 16 years and is now in its 17th, is usually marked by violence and mass arrests.
Last year’s ended in 226 arrests.
“Fifteen times over the last 16 years, we had riots that happened at the end of it,” said Montreal police spokesman Ian Lafrenière.
“We’re hoping for the best, but we’re getting ready for the worst.”
Lafrenière said the annual protest’s recent descent into violence is partly due to fewer activists and more troublemakers hitting the streets.
“It looks like a sport now. Some people are coming to different protests because they want to have a good time,” he said.
Organizers of the anti-police brutality march have always refused to give the police their itinerary.
A municipal bylaw allows police to declare a protest illegal if no itinerary is provided ahead of time.
The police will hand out flyers advising public transit users to avoid using the metro around evening rush hour.
The demonstration is set to begin at 5 p.m. at the corner of St-Urbain and Ontario streets, near the Montreal police's downtown headquarters.