Two men posing as tourists hired the chopper for a tour, said a reporter from LCN television network who said he knows the pilot.
Once they were in the air, the men held a gun to the pilot's head and reportedly ordered him to fly to Saint-Jerome.
Quebec provincial police spokesman Benoit Richard would not comment on the reports.
Reaction time 'probably too slow'
Once at the detention center, the helicopter hovered as two inmates climbed aboard using cables or ropes lowered for them, police said.
Slack-jawed prison guards watched as the helicopter then spirited away as two of their prisoners clung on.
One of them, police said, was 36-year-old Benjamin Hudon-Barbeau who had beaten a double murder conviction on an appeal. But he was in prison in connection with an attempted murder investigation.
The other, 33-year-old Danny Provencal, was serving a seven-year sentence for various offenses, including arson, police said.
The prison, which houses 480 inmates, knows how to handle the expected. About a month ago, it quelled a riot before it got out of hand.
But, Yves Galarneau, the deputy director general of Correctional Services Western Quebec, said he'd never seen anything like this escape in his three-decade-long career.