I only know US border control considerations and they can only legally ask for access to what you have on you when you cross the border. If you are an American citizen (or permanent resident) you can decline, and they may well seize your device(s) but cannot deny you entrance. If you are a visitor to the US they can legally deny you entry if you do not comply with their vague and ever changing requests.

But in neither scenario could they legally demand access to a backup copy: they can only ask for access to items in your possession while crossing the border, otherwise they would need to get a warrant.