Environmentalist David Suzuki, actress Jane Fonda, author Naomi Klein and former diplomat Stephen Lewis will be among the notable names in the crowd, which will also include members of First Nations, UNIFOR, the Ontario Federation of Labour, the Registered Nurses' Association of Ontario, Toronto Regional Labour Council and Greenpeace Canada.
"This is the kind of coalition that will make the difference," Fonda told the crowd. "They are saying we don't have to choose between the environment and the economy. That's a false choice. In fact, renewable energy — doing away with the fossil fuel-based economy — will create more jobs, more democracy and more justice."
Fonda, who took part in a similar rally last month in B.C., recently told CBC News she added environmentalism to her many causes after reading Klein's book This Changes Everything.
"It's really very simple. We cannot drill anymore. All the fossil fuel that's in the earth has to stay there now," she said in the interview. "We have enough already. Big oil doesn't know that word, 'enough.'"
The march started at Queen's Park at 1 p.m. Demonstrators will head south on University Avenue, head east on Dundas Street, and north up Jarvis Street to Allan Gardens.
The demonstration comes ahead of a three-day summit meeting in Toronto of North and South American leaders and environmentalists on climate change.