Also starring in the pantomime are Hollyoaks actor Nick Pickard and TV veteran Cilla Black.
Former soap star Ellison takes on the lead role, while Dennis will play Buttons. Pickard has the role of Dandini and Black is cast as the fairy godmother.
"I think people are gobsmacked that we have all come together," Ellison told The Sun. "But it will be such a laugh. It'll be as camp as Christmas."
Pickard commented: "I'm sure the Hollyoaks cast will be there to heckle me."