A crowd estimated at more than one million people gathered across downtown Toronto for a parade in tribute of the team, but the victory rally at the jam-packed square was briefly halted by gunshots, AFP reported.
Toronto police tweeted that two victims had serious but not life-threatening injuries, two people were in custody as a result of the incident and two firearms had been recovered.
Footage shared on social media showed dozens of people scattering from the area behind the stage.
But with a crowd of 65,000 packing the square, the celebration went on with only a delay of about two minutes, with Canadian Prime Minister Justin Trudeau joining the team on stage to celebrate the Raptors' success.
"Raptors fans, every day you showed what Canada is made of, people who believe," Trudeau told the rally.
People had begun camping out overnight to fill the square, so many that police told people to avoid the area. Subway stations were closed to limit access.
In a super-sized version of the crowds that packed "Jurassic Park" outside the team's arena to watch game telecasts, supporters filled the square after more than two hours of delays because spectators spilled onto the parade route to witness players ride by on open-topped buses.
"You think the parade is going to be amazing and you can't even picture this," Raptors coach Nick Nurse said.
"It's pretty cool."
The Raptors beat defending champion Golden State 114-110 on Thursday in California to capture the best-of-seven NBA Finals four games to two.
"It's amazing," Raptors star Kawhi Leonard said.
"Everybody is out. I don't think anybody went to work today. Everybody got the day off. Look at it. It's crazy.
"Thank you Canada for the support. We did it."
NBA Finals Most Valuable Player Leonard said the team has been celebrating ever since they ran off the court in Oakland.
"The last few days have been amazing," Leonard said.
"No sleep. A lot of celebrating. And we're going to keep going."
Players wore T-shirts, sunglasses and held cigars as they watched people line Lake Shore Boulevard and York Street.
"This is why we wanted to win a championship," Raptors guard Kyle Lowry said.
"This is unbelievable. And we ain't even close to being done."
In the ceremony, a roadway near the arena was renamed "Raptors Way" and Leonard accepted the key to the city on behalf of the team to chants of "M-V-P."
"This thing is so special because of you guys," Nurse told the crowd – moments before the shooting briefly halted festivities.
'Joy on people's faces'
The last time Toronto celebrated a major North American sports title was in 1993 when the Toronto Blue Jays won baseball's World Series.
Canada, a country of 37 million, had 20 million people watching the telecast of game six.
Fans enjoyed their moment with players on Monday, with chants of "Let's Go Raptors" popping up along the route.
"I didn't think there were this many people," Raptors swingman Danny Green said. "It's amazing. This is our way of trying to give back to them. It's special."
Toronto Mayor John Tory declared Monday "We The North" Day in Toronto, using the team's slogan.
Spanish center Marc Gasol looked out over the sea of humanity and marveled at the scene.
"How much joy you see on people's faces," Gasol said.
"It has been a great ride. I can't imagine a better ending to it."
Crowds were so huge on University Avenue they filled the street and blocked the path of the parade for more than half an hour.
"This is crazy man. I don't know what else to say. It's crazy," said Cameroonian forward Pascal Siakam. "It's an amazing moment."