Last time I was there, Cannes had rental cars (Europcar).
LOWG / GRZ / Graz
Train is located a few minutes walk from GAC exit and takes you to the center in 10 minutes.
Bus is located directly outside the terminal.
http://www.flughafen-graz.at/en/terminal/anreise-parken/bus-bahn.html?type=%3Fsub%3Dab%3Fto%3Fsub%3Dan
https://www.graztourismus.at/en/see-and-do/sightseeing/top-10-sights
App2Drive doesn’t accept alphanumeric postcodes.
So no luck for us from UK.