L.R.
E., it's very tiring, wow, we've all been there! But unfortunately you may have to deal with it for some time to come, and it could improve for a while only to return. Ages three to five (younger or older in some kids) are very often typical years for periods of nightmares, unexplained waking and even "night terrors" (which it does not sound like your son has, and be glad--see an earlier posting recently about night terrors and you'll see why).
Having him cry it out or stand at a gate in the middle of the night only wakes everyone else and makes him much, much more awake, which probably makes him harder to get back to sleep. Asking him questions or trying to reason with him at 3 a.m. stimulates him too. I'd gently, quickly guide him right back to his bed as soon as he appears, with minimal talking or stimulation except quietly telling him you're there for him. Make sure he lies down and stay and rub his back or stroke his arm--whatever works for him--until he's back asleep. You might find he returns top sleep much faster. Yes, you'll have to get out of bed, but all of you may get more sleep overall.
Crying it out or keeping him in his room won't do much in the wee hours except make him believe he's done something wrong by trying to come to you, and you do want him to feel he can come to you when he's scared by day or by night.
I'd just return him to bed swiftly but keep things calm and quiet so he'll know his bed is a safe place to be and you and his dad are safe havens when he's scared or wakeful and doesn't know why. Good luck.