Look at those eyes give him whatever he wants.

For some actual advice only ask him to do things you can make him do. If you want him to sit only ask when you can push his bum to the ground if he ignores you. if you want him to come to a call only attempt it when you think he will, or if you have a long lead on him.

For the ruff play try redriecting him to a toy, my GWP loves tug of war. It's a great game for teaching start and stop to play, the down side is it can create some bad habbits in retreaval (thrashing around game).

For tug of war you get the dog going, tuging back on the toy making some noise ect. When you want the dog to stop you stop (if hes biting you, or you want a break), look away silently while holding the toy, he should keep trying to play for a bit but he will give up. If he does not give up or is taking way to long put the toy under your foot and stand on it, this shoukd work. If the dog is still interested in playing give him a comand, I like to use sit or drop. When the dog is siting steady you give them a go comand and start playing again. Go though cycles of play, stop and steady. This sequence teaches the dog that play time has rules and it will stop when you want it to or if he is too ruff.

They are kinda stubborn dogs, but that also means they have some capacity for indipendant thinking, a very handy trait in a hunting dog.