1. If he had played during Lebron's time, he would have studied him and figured out how to neutralize and beat him.
2. He would have tried to tear Lebron apart mentally with his constant taunting and trash talking.
MJ was sociopathic in his competitiveness. It drove some of his teammates into the ground because he made sure no one else would be able to get into their heads. He worked Ewing. He worked Barkley. And yes, they worked him too sometimes. But I have no doubt that Jordan would have been up to LBJ's challenge, and I have no doubt MJ would have beaten Lebron in the finals.