K.W.
I think you should let it go. If you have tried everything you know, he is not ready. I went through the same thing with my 3 year old just before preschool and was sick with worry because they do not allow non potty trained children. But, like you said, I couldn't force him to go on the potty and my doctor said that would just backfire anyway. He was fine with the peeing part but would say no every time I asked him if he wanted to go poop on the potty. So eventually I got him to wear underwear and when he had to poop he would tell me he wanted a pull-up. I let him do this for as long as he wanted and it was only a few weeks and one day out of the blue he said he wanted to poop on the potty. He never looked back. It will happen when HE is ready, don't worry! My doctor said average age for boys to be potty trained is 3 1/2 and that is about what my son was. Good luck.