2 ways I see this fight going. Scenario 1: Anderson is a counter striker, but GSP is very quick at getting in the pocket doing damage and getting back out. I believe that could cause AS some problems and may even frustrate him. And as the fight wears on, GSP will secure takedowns and out wrestle him on the ground. And yes I know that Anderson has great BJJ, but GSP's wrestling will neutralize that. GSP gets his hand raised.
If Anderson not only pushes the action, but comes HARD at GSP, I believe Anderson can get a KO. GSP does not do well when he's stalked.