My son is 3 years old. Every night he goes to bed in his underwear and the problem is he doesn't wet the bed but holds his need to urinate and you could tell when he's sleeping he's really fighting and not sleeping well. We tried waking him up at night so he can go to the toilet but he cries and refuses to go. As, sleep is really important in a kid's life. I really hope I can get some advice.
We didn't have the exact same issue, but for what it's worth, before our 3 year old could make it through the night on her own, there were several months where we carried her to the toilet when we went to bed, a couple of hours into her sleep.
We would put her on the toilet, and she would go, and we could carry her back to bed without waking her up. From your description, it sounds like you might be able to do the same, if waking him up is the hassle. If you can endure it, this might be an acceptable workaround until your child grows a bit older and learns to self-regulate this.
kids are very different so there is no single answer that would be the right one.
A few suggestions are:
make sure he drinks enough early in the evening, not directly before going to bed.
make sure he uses the bathroom before going to bed (even if he says he does not need to, make it a routine, it is fine if only little comes out). If he does not want to go, make it fun (sing a song, tell a short story or invent a joke as part of the routine).
I would recommend not to wake him. As you say, sleep is important. Kids sleep deep and can get very confused. They can be half awake half dreaming. Usually if they sleep at night, let them sleep. (This is also true for night terrors, where they seem to be awake, but are not - don't wake them, sing a song, hold their hand, talk to them calmly and eventually the terror goes and they sleep deeper again).
Many kids at 3 years are perfectly fine sleeping through the night without going to the bathroom.
If he really has to pee at night, he will not be able to controll it and will wet the bed. So if the bed is dry the next morning, he is fine.
If he seems like he is "fighting" it could be a dream, maybe too much TV, action not appropriate to his age etc. Or maybe just normal dreams, many kids are not calm sleepers, especially that age.
And as mentioned above, if you are unsure or if he wakes frequently at night, is scared and cannot fall asleep again, talk to a doctor.
Potty training is a complex subject and it has to come from the kids, forcing it can make things worse. All the best.. also this period will pass.