Nearby, earlier the same evening, a teenaged boy was slashed with a machete during a fight at the the Forks skatepark. The boy was taken to hospital in stable condition.
It was all part of a busy night for police, with nearly 800 calls for service, said spokesman Const. Jason Michalyshen.
The men stabbed at the gang fight were all upgraded to stable condition on Thursday, police said, adding that a fourth man was also injured after being assaulted.
That brawl happened in the parking lot of Earls Restaurant on Main Street, which was surrounded Thursday morning in yellow police tape. Blood stains on the pavement as well as a switchblade were marked by police evidence tags.
Police said 300-400 people were in the fenced-off lot for Canada Day celebrations. The event was billed as the fourth annual Canada Day Block Party, "just steps away" from the main events at The Forks.
The violence erupted just after midnight — at about 12:40 a.m.
The police service's organized crime unit is investigating.
The machete attack at the Forks happened at about 8:30 p.m., as thousands of people gathered for Canada Day.
The teen and another male were fighting with a large crowd of people around them when a third man jumped into the mix and slashed the victim with the big knife.
Winnipeg police investigate Canada Day stabbing at The Forks
A 20-year-old man has been charged with:- Assault with a weapon.
- Possession of a weapon.
- Failure to comply with court conditions.
The fight was caught on cellphone video by one of the witnesses and posted to Facebook. The police said the video helped in their investigation.
Forks spokeswoman Chelsea Thomson said there was close to 100,000 people there — one of the busiest Canada Day events at the site in nearly 20 years.
"For the most part, everything went really well, so it's really unfortunate that this has to scar what would have been an otherwise perfect day," she said.
"We take public safety very seriously here at the Forks every day and even more so on Canada Day. We work very closely with the Winnipeg Police Service."
Violence in 2014
It's the second year in a row that Canada Day was marred by violence in Winnipeg.
Last year, a 28-year-old woman was shot and killed on Donald Street, just off Broadway.
As well, two people were stabbed near the Via Rail station — not far from where Wednesday incident happened — leaving a 25-year-old man dead and another man in critical condition.