Are bear canisters required for backpacking?

In many regulated areas they are mandatory. Parks such as those in the Sierra Nevada, parts of the Adirondacks, and other high-use wilderness zones require an approved hard-sided container, and rangers can issue citations for non-compliance. Always check the specific land manager's rules, and look for IGBC (Interagency Grizzly Bear Committee) approval, which several products here advertise.