The incident occurred late last night when the driver of the bus going to Delhi from Farukhabad lost control over the vehicle and it fell into the canal in Pilua area, they said.
While bodies of 21 people were fished out from the canal, 23 others were saved by the locals and a police team.
Among those killed included 11 of a family, including a newly-wed bride, going to Ghaziabad from Aliganj after the marriage ceremony.
According to the passengers, the driver of the bus was in an inebriated condition.
Some passengers are said to be missing and police was trying to trace them. Their exact number is yet to be ascertained, Etah District Magistrate Lokesh M said, adding relief and rescue operation were on.
Those killed included 10 men, four women and seven children, SSP Radheymohan Bhardwaj said.