The safety rules for work hours have been known for ages, so this is not a new challenge for management.

Yes, but this has to be less of a problem when they've been canceling tons of flights, right?

Depends on the specifics of the duty time rules and how the flights were canceled. If the crew showed up and started getting the flight ready, but the flight was cancelled before takeoff, that may count as duty hours and could reduce their availability in the near term.

If the duty time rules only count time after takeoff, or only time after doors are closed, those both offer a different set of times.