Is there a difference between You are Elsa and Are you Elsa
"Are you Elsa" is a question. If you want to ask that in Finnish, you'd say: "Oletko (sinä) Elsa?"
You are Elsa = Sinä olet Elsa (you are just saying that the person is Elsa)
Are you Elsa is a question. You ask if the person is Elsa = Oletko sinä Elsa?