The rally was held for Makoon, a five-month-old black bear cub that weighs about 14 kilograms.
Makoon is at the zoo and is due to be released back into the wild soon, a move the protesters do not support.
Judy Stearns, who started an online group dedicated to stopping the bear from being released into the wild, said more than 10,000 people have signed an online petition protesting the release.
She said a bear sanctuary in Ontario has offered to care for him.
Manitoba Conservation wildlife director James Duncan has says Makoon is thriving and has gained weight and is nearly ready to return to the wild.
Duncan has said the bear has a 50-50 chance of surviving in the wild.
Conservation Minister Gord Mackintosh has said he will take his advice from the experts in his department.
The province has said they can't give Makoon to a haven at another province over fears of spreading disease. Officials said Winnipeg's zoo is not equipped to handle adult black bears and many other zoos already have enough black bears, because they are a common animal.
But Stearns said she fear young Makoon will become prey to predators if he is returned to the wild.
"It's not just because he's a cute, cuddly bear cub," she said. "I don't like to see any living being... tossed out into the wild to suffer by our own government."
The cub was found abandoned near the side of the road earlier this year and taken home by Rene Dubois, who cared for him until he was seized by Manitoba Conservation.
The cub was then sent to the Assiniboine Park Zoo to be rehabilitated.
(Winnipeg Free Press)Suggest a correction