I have the regular, direct, Paramount+, and I don't see Big Brother Canada. Are you in Canada? When you watch a subscription service through a 3rd party channel like The Roku Channel (or Amazon Prime), databases can get mixed up or just be wrong.
Subscribing through something like The Roku Channel is the worst way to subscribe, as it only works through that. Subscribing directly to Paramount+ on their web site will let you watch on multiple devices.