The accident happened at 3:50 p.m. local time on Friday when the second floor of the bus struck the roof of the Westboro bus station, which is located in the city's Westboro neighborhood.
The investigation will take a long time and likely would mean the closure of the busway and nearby roads for at least many hours, Bordeleau said.
Sgt. Cameron Graham from the collision investigation unit, the team overseeing the investigation, told reporters on Saturday they're exploring a number of aspects, including "human factors", the vehicle itself and weather conditions.
Afternoon traffic snarled around the station as dozens of emergency personnel descended on the scene.
Monica Lung was on her daily bus ride home from Carleton University in Ottawa when she passed the horrific scene at Westboro station, where a double-decker bus jumped the curb and smashed into the transit shelter.
The investigators worked all night to identify with certainty the three victims and to make contact with their families and loved ones.
They will also have to survey the wreckage using drones, go over video and data gathered from the bus and bystanders, said the police chief. Of those transported, 14 were in critical condition and 11 were in serious condition, paramedic chief Myles Cassidy said in the news conference. This particular bus was not scheduled to stop at the Westboro station, which is another aspect being probed in the investigation.
Officials from Transport Canada and Ontario's Ministry of Transportation are also investigating.
OC Transpo, which is in charge of Ottawa's public transportation, tweeted on its verified account, "Buses are being detoured as a result" of the collision. "A lot of people screamed, the people in the front were trapped under their Seats". "Thank you to the first responders who rushed to help - we're monitoring the situation closely".
The bus was nearly at its 90-passenger capacity when the crash occurred, police say.