R.Y.
Has he given you any reason he doesn't want to grow up? Is there a new sibling in the house (by new I mean born any time since you started training him)? Any other big changes? If not then it is a matter of picking your time and switching to underwear.
At this point maybe you want to take a potty training vacation and start again after Christmas. Maybe after a break you will both be more willing to try and cooperate. That is kind of what I did with my son. I had him in pull ups from 2.5 but he wasn't ready at first then I had another baby and that whole adjustment. My son is a February birthday so he was just under 4. I put him in underwear and was able to be mostly home for the Christmas vacation. The first 2 weeks there were a lot of accidents and I went back to pull ups one week when he was sick that winter.
I read one of the sites posted by Peg M. I think the author is right--frequent reminders to use the potty fuel the power struggle. That was part of the problem with my son at least. At 4 my son could go 2-3 hours and stay dry. When I figured that out I cut down the number of potty breaks substantially and tried to use natural breaks in the day. I tried for a while using a timer for every 2 hours so I wasn't nagging him about it (it helped a little). He still argued (he is just that kind of kid). Eventually I did give him time outs for refusing to follow directions and take a potty break--but not for accidents. I'm not sure how much it helped; that was partly my frustration. I also gave consequences for when there was an accident and he didn't change immediately or ask for help changing (like at preschool).
Anyway, I don't know if any of the above will help but you are not the only one struggling. I'm kind of dreading the process with my daughter but at least she is a more cooperative kid most of the time.