An estimated 200 members of far-right groups and 100 counter-protesters lobbed expletive-laced insults at each other on the snow-covered lawn, resulting in one arrest.
Scuffles erupted just as the event got underway, but riot police quickly separated the two sides. The crowd then began chanting "Reject immigration pact," but was drowned out by shouts of "Shame" and "Refugees welcome, racists go home."
Sylvain Brouillette, spokesman for the protesters, said the United Nations pact risks eroding sovereign immigration policies -- a view echoed by opposition Conservative leader Andrew Scheer, and conservative politicians in other countries, but roundly dismissed by its proponents.
"Canada was built on immigration. We have learned to live together and we have found a way to do it well, so we don't need a UN migration pact to tell us what to do and change a system that works," Brouillette said.
Passerby Aditya Rao stopped to listen to the arguments but concluded that the protesters were misguided. "It boggles the mind," he told AFP. "These people are grumbling about all the chaotic migration, but at the same time are complaining about an effort to make it orderly and safe. It's atrocious."
The non-binding pact is due to be formally adopted at a December 10-11 conference in Marrakesh, Morocco.
It lays down 23 objectives to open up legal migration and better manage migratory flows, as the number of people on the move worldwide has increased to 250 million, or three percent of the world population. Among its principles are the protection of human rights, including those specific to children, and recognition of national sovereignty.
Its objectives also include helping countries deal with migration by sharing standards to improve information and integration. The US quit talks on the pact last December, and several countries including Hungary, Austria, Poland, the Czech Republic, Slovakia and Australia also rejected it.
Immigration has become a more polarizing issue in Canada, where the number of refugee claims last year nearly doubled compared with the previous year.
In Ottawa, former Conservative foreign minister Maxime Bernier, who broke with the party in September to start his own, has gathered 48,000 signatures on a petition to limit immigration.
"Canadians want their government, not foreign entities, to be in control of our immigration system," Scheer said during a faceoff in Parliament with Prime Minister Justin Trudeau, who vowed to sign the UN pact.
"Welcoming people through a rigorous immigration system, from around the world, is what has made Canada strong, and indeed something the world needs more of, not less of," Trudeau countered.
In late 2017 Canada's Immigration Minister Ahmed Hussen said his country will boost immigration to one million over the next three years. Canada has seen a rise in asylum seekers since its neighbour the United States elected President Donald Trump, who has tightened US immigration policies.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)