Fry who began his playing career at United is stepping down as Posh chief at the end of the season and it will mark the end of his 31-year career in management.
"It's a great personal coup for me, it will be a superb night for the fans and the club should benefit financially as well," said Fry. "I started my career as a player at United so they are the perfect team for me to finish against. It's a brilliant gesture by Sir Alex Ferguson to agree to bring his team down."
"Sir Alex has always been very generous towards me and he has guaranteed that I have an exciting night to mark the end of my career."