According to Variety and Comics2Film, the upcoming Garfield movie will have Bill Murray as the voice of Garfield. Apparently, Garfield the cat will be CGI, as will probably be Odie and any other animal characters.
I need to point out a cool bit of synchronicity here: the voice of Garfield until now was the late, great Lorenzo Music in the Saturday Morning cartoon. Now it will be Bill Murray in the movie.
Bill Murray played Peter Venkman in the Ghostbusters movies, and Lorenzo Music voiced the character for the Saturday Morning Ghostbusters show! There must just be something very compatible about these guys!