If Germany has make peace with Stalin on eastern front will operation Overlord still be successful?

Answer 1

It would have taken much longer to proceed from the landings on the Normandy Peninsula to final entry into Berlin. The Soviets had destroyed 80% of Germany's air and armored assets by June 6, 1944.
So, Operaton Neptune (the Naval phase) and Operation Overlord (the landing phase) would have been successful. It was the push further inland which could have slowed things up quite a bit.

Answer 2

Probably not. The Germans would have had many more Panzer Units in Normandy.