Witnesses delivered conflicting reports about how the boy was injured at the Red River Ex amusement fair, CBC News said.
Some said they saw the boy fall from the second tier of the Crazy Mouse roller coaster.
Garth Rogerson, chief executive officer of Red-River Ex, said other witnesses indicated the boy may have jumped off the ride onto the tracks.
"I hate to say that because it is speculation, and we want to be respectful to the family. He is in very, very serious condition," Rogerson said.
Witnesses told the CBC the boy was bleeding profusely.
"The [ride] stopped and I heard a lot of people screaming, and I looked forward and I saw blood," said Johnathon Ginter, who was on the ride at the time of the accident.
After the ride was stopped people were stranded on it for nearly an hour, officials said.
Rogerson said there was no mechanical failure on the ride.