It sounds like you are living my life. I have a 3 year old and we started training in the fall.... he doesn't throw fits but he just has no clue as to when the pee is coming. He was poop trained but I stopped it all cause he just wasn't getting it. No, last week I tried again and it was worse than before. Now he doesn't want to do anything on the toilet. So I am waiting until summer when he can run naked in the backyard and see how good it feels to not wear a hot sticky diaper. I Pray that works cause I have tried everything else. I am not usually the kind to let my kids run naked but this is a last resort.
It sounds like your son may simply have a hard time with change. At 3.5 I would think he would understand the feeling. These are some other ideas.
Put him in underwear and allow him to get them soiled and let him sit in it unitl it is uncomfortable on him. You may need to do this a few days. You can put plastic pants on him so it doesn't get all over your house.
You can just wait until he needs to be trained (before school begins)
You can ask him what reward he would want for doing something especially good (don't tell him it is potty training). Let him choose then tell him when he can sit with a good attitude, he will get this reward.
I think baby steps of success is important to celebrate for a child who is emotional about it.
They say never discipline for potty issues but because of my experience I am thinking otherwise. I actually stoped training cause I was getting too angry with him. I will pick it up again later and even then he needs to take ownership of it I can't make him. I refuse to battle with him for months over it.
They do say boys are much more difficult to train than girls. Now I see that. I just didn't think it would be MY boy! lol.
Hold on. This too shall pass.