My daughter had a root canal of her two front teeth when she was two. It was a cavity at the gum line, and she needed her front teeth to bite... If it hadn't been her front teeth I would have said to pull them.
They gave her a dose of liquid medication, ( a sedative) and we waited for it to take effect. She was put in a papoose which is a Velcro harness attached to a board to "swaddle" the child during the procedure ( I don't know if your guy is too old for that. They gave her nitrous and Novocaine, and it would have been fine if they just hadn't strapped her into the papoose,, She struggled against it so !
She had caps on her teeth till they fell out at around the age of 6. It was really hard on me, and she still remembers feeling frightened, But that's because of being restrained, not the root canal itself.