A Radiohead show that was to have been held on the stage in Downsview Park was canceled, the Toronto Star reported. Organizers said ticket-holders will receive refunds.
The collapse occurred about 4 p.m.
Fire Capt. Mark Strapko told CNN scaffolding fell 40 feet to the stage.
Two people received minor injuries in addition to the person who was pronounced dead at the scene and a second taken to a hospital.
"It was a really, really loud noise," Amy Kang, working at a beer tent about 300 feet away, told the Star.
The Radiohead concert was one of the acts in the North by Northeast music festival now under way in Toronto.