Many kids are simply not neurologically or emotionally mature enough to complete potty training until they are three, or sometimes older. Boys tend to train later than girls, and age 3.5 is not uncommon. Toddlers often simply don't recognize the signals until it's too late – their is so much going on in their little worlds that's more interesting. Even if you can coax children to train earlier than their natural inclinations, kids get overwhelmed by looming parental urgency and expectations, or the simple size of the commitment, and regression or prolonged training is more the rule than the exception.
Allowed to proceed at their own speed, kids show interest when they are ready without urging, or even surprise their parents by announcing when they know they are ready. And then they are. Children WANT to train when they are ready, just as they WANT to walk and talk when they are ready.
Comparing your son to your daughter will only become a source of unhappiness for you both. Your little guy sounds like he's getting there, but your eagerness is thwarting you both. Putting him in diapers won't confuse him if you tell him you trust him to learn to use the potty when he's ready. He will appreciate your trust in his ability to grow up just right.
Success rides on considerably more than the simple physical ability to use the potty. There is a level of emotional willingness and motivation – a maturing of the child's impulsiveness and distractability – that really must happen before the child can complete this developmental step, which will be a satisfying source of pride once he is ready to make it.
Your son will start to let you know when he is mature enough. He'll show more interest himself, ask more questions, want to prove his new ability. Earlier attempts at training very often results in regression when the full size of the obligation hits the child. Three or older is not unusual for kids, especially boys, to thoroughly want to be out of messy diapers and into big-kid undies.
Before then, it is more likely to become a source of anxiety, frustration, and resistance. If I were in your situation, I think I'd be inclined to wait for the child's cues. He won't be confused if you simply let him stay in diapers for awhile, and when he's fully ready, he won't need your constant reminders to go, so life will be easier for both of you. And when he's ready, he won't need rewards, either, though a celebration might be in order.
Potty training is as natural, and as desirable for the child, as learning to walk and talk.