I have a database on the Desilets family but I can't link your grandfather. I have no doubt that the family came from Quebec since it is where the Desilets surname was "invented".
Should you find any additional detail or clue, get in touch, I'd be happy to try again.
Here are some suggestions for more clues: - Try and find your grandfather's death certificate. - His marriage certifcate. He was likely Catholic. Check the church records. - Check the church birth records of all his children. The Catholic church baptism records will show the name of the godparents who are most of the times relatives of the parents and they can provide good clues. - Check for information within your family. Check with old aunts and uncles. Old aunts often have little black notebooks or bibles with information.