My 6 yo grandson had a root canal as well as other major work done. The first pediatric dentist said that they would have to give him general anesthesia because he is very active and has difficulty sitting still. We took him to another dentist who specializes in being as pain free as possible. He did the work in 4 sessions without general anesthesia. He uses a drug that sounds like it might also have an anti-anxiety component. My grandson got bored but never complained of pain.
I've had several root canals. They weren't any more painful for me than having a filling. They did take more time.
The dentist my grandson goes to spends the first visit gaining the child's confidence. They cleaned his teeth and would've taken x-rays if they other office hadn't sent the ones over that they took. This dentist has written a booklet on pain free dentistry for children.
I recommend that you find a pediatric dentist who is concerned about the comfort of his patient. Make an appointment to for an exam and have the dr. discuss what will be happening with both of you. If you can reassure him that the pain will not be so bad, tho there will be some that will help. You can tell him that once this is done the pain will stop.
I noticed, during this experience in which I took my grandson to 3 different dentists (the first one doesn't do major work) that it makes a big difference in the dentist's philosophy and ability to get along with children. The second dentist specializes in pediatrics and major work. My grandson squirmed, wouldn't stay in the chair, was in general very difficult. He'd been compliant and easy with the first dentist. He was back to being co-operative with the third one who did the work. He does have behavior issues which the first and the last dentist managed very well. The dentist's skills with children is as important as their skills with dentistry.