On the main Roku web site, you can do a keyword search for a channel (https://www.roku.com/whats-on). But that is going to return channels available in the US. Depending on your location, Roku may have a country-specific web site that offers more localized search. There are also a number of web sites that offer lists of favorite channels, but again they may be country-specific.
I would be very careful offering guests access to channels that you pay for, unless those channels don't have on-demand purchasing ability. Someone could really run up your account bill with pay per view. And what one person watches could influence what the next guest sees on the screen.
Dan
Roku Stick (3600), Ultra (4640), Ultra (4670), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.
