Use the search feature. This has been done and re done several times. Depends on Galactus power level and which Celestial. Normal powered Galactus could take most Celestials except Exitar, TOAA and Arishem. A fully powered Galactus could beat all of them combined. A very hungry Galactus would be in trouble against any of them.
http://www.killermovies.com/forums/showthread.php?s=&threadid=389543&highlight=Galactus+vs+Celestial
http://www.killermovies.com/forums/showthread.php?s=&threadid=358216&highlight=Galactus+vs+Celestial
Use one of those. There's been others, but those are the first two I found. And please try to use the search in the future. Thanks. 🙂
Closing.