I am not native speaker but i think "may you be happy" is the most correct

May you be happy. This is a little formal... no one says this in normal conversation. It might be written in a card

"May you be happy" is the correct way to say it, as Sven stated. A better way to say it would be, "may you always be happy". Here are some common wishes using the word "may". 1. May God bless you. 2. May you always be successful in life. 3. May all your dreams come true.