Since "Germany" or "Germania" worked for two Germania territories I thought that "Gaul" might work for the several Gallia provinces, but it did not. I also thought "Spain" or "Espana" might work for the two Hispanias, but it did not. Also Britain works but not Brittania?
Britannia does work as long as you spell it correctly. One t and double n.
Romans: Let's be all three!!!