Radio-Canada says autopsy results from Thailand indicate Audrey and Noemi Belanger died after consuming insecticide.
Twenty-year-old Audrey and 26-year-old Noemi were found dead at a beach resort in the Phi Phi islands last June.
Autopsies were performed on the bodies in Montreal but the results have not been released.
Carl Belanger tells The Canadian Press he is convinced his daughters did not know what they were consuming.
He says two other young Quebecers who spent time with his daughters told him they all drank alcohol together.
Belanger wants a full inquiry, particularly as other tourists are believed to have died in similar circumstances in Thailand.