Toronto police said the man, 40, was not wearing a helmet when he fell near St. Clair and Wychwood avenues at about 5:30 p.m.
Janet Calder, who witnessed the accident, said the bike got caught in a stretch of streetcar track. "The track held on to the wheel, it threw him, he fell on the concrete, split his head open," she said.
EMS said the man was pronounced dead at the scene, though police haven't determined whether the fall or a medical condition led to his death.
Sgt. Glen George, standing near the apparently undamaged bike and the man's shopping bags, stressed safety afterward.
"I'd just like to impress upon the public the need to be wearing a helmet when riding a bicycle and also to keep their hands free," he said.
About two months ago, Ontario's deputy chief coroner released a report on more than a hundred cycling deaths that said helmet use by all cyclists can decrease fatal head injuries.