I think a person's personality will always shine through no matter what they are doing. If a man has a great personality, chances are, he will have what it takes to be a great dad. And the opposite is true as well.
So, if a man has a great personality, and he is willing to be a dad, then more than likely, he will be a great dad!
As far as being a great dad is a piece of cake, well ... with the challenges of being a dad in today's world, I think it will take several pieces of cake to pull that off.