Actually, Easter is not common festival , it jsut religous fastiva in Korea. So,even though I am a christian, but I have never heared 'Happy Easter greetings'

Happy Easter..actually there's not a popular term for this except merry christmas! (this term itself is very widely used) in Korea. However, I think the terms I'm gonna say have most possibility to be understood for Koreans. 'Happy Easter, peace be with you: - 행복한 부활절 되세요. 평안이 있기를! - 축복된 부활절 되세요. 평강이 있기를! If you've got further questions about this, ask anything you want. lol