Let him decide, if he chooses to stand up, pop a 'ping pong' ball into the loo, he will have great fun trying to hit it, and it will help him to control direction (if you know what I mean!. If he chooses to sit then that is ok too, but you will need to make sure his willy is pointing downwards in to the loo otherwise he will surely miss and wee all over the floor.
Thank you for your replies.
I am a single parent so he can't watch his father urinate.
I think I will sit him on because he has always sat on his potty to poo and wee and he has seen me or should I say heard me sit on and wee.
I will remember to make sure his willy is pointing downwards.
Yeah it is very important to have it point down, i have a 7 year old who sometimes sits to pee and it ends up all over the whole bathroom. But afer he gets used to sitting and peeing and used to using the toilet, I would have him try standing so he gets used to it too, public restrooms are often nasty and haveing the privilage of being able to stand rather than touching the gross toilet would be awesome, I wish I could do it.
My son used to wet the bathroom floor because his wee was finding its way under the toilet seat and then trickling down the front of the bowl and onto the floor. It also used to wet the back of his pants.
It was my fault for not holding his penis down.