If it’s predominately a Jewish community, then HAppy HANNUKAH is appropriate....otherwise it’s Merry Christmas.
How about just "Have a Happy and Merry Hannukah Christmas or Christmas Hannukah as you like it". There is a way to do it like this. It might depend upon whether the knishes or ham comes to you first.
'Happy Holiday' is what English folks say to someone that called in sick to work and is otherwise having fun.