As in all things, listen to your PH, and follow his or her directions! Typically, the rifle will be carried with cartridges in the magazine but with the chamber unloaded until the PH directs. The PH will walk ahead of you, and in areas where dangerous game might be present, his or her rifle will usually be fully loaded and ready. Yours doesn’t need to be until you are “action imminent.”
The basic rule is that the chamber should not be loaded unless you can absolutely control the direction of the muzzle. This means that if you are carrying the rifle slung over your shoulder, the chamber should be clear. In areas where dangerous game is present, most PHs don’t use rifle slings; they carry their rifles in their hands, and the rifles are always ready.
Most sport hunters do use slings, and that’s fine. But a fully loaded rifle should not be slung because it is impossible to control the muzzle in the case of a slip or fall, and many mechanical safeties can be brushed off by clothing while a rifle is slung. If in doubt, never hesitate to ask your PH if you should chamber a round.