The bus had collided with the Bridgewater Canal Aqueduct on Barton Lane in Eccles on Monday, with the top level of the vehicle being torn off.
A passenger was also ejected from the top deck of the bus.
Greater Manchester Police said that the driver, a man in his 50s, has since been bailed pending further investigations.
Three people – a 19-year-old female and two men, aged 20 and 40 – who sustained serious injuries remain in hospital in a stable condition.
Seventeen others were treated at the scene for injuries.
A major incident was declared by North West Ambulance Service after the incident, with 10 emergency ambulances, advanced paramedics, the Hazard Area Response Team and North West Air Ambulance dispatched.
Officers believe the bus had come off its expected route. They also think height restriction warnings, including hanging chains and signage, had not been complied with before the crash.
Transport for Greater Manchester said the bus was a 100 service and was in operation at the time of the incident.
The service departs from Shudehill and travels to Salford, Trafford Centre, and Warrington.
The location where the incident took place did not appear to be on the Bee Network Route map for the 100 service.
