With today's release, you are now able to look up canceled reservations. Simply go to the reservations tab, and then click "Canceled" to access the canceled reservations.
The reservations are sorted by the most recently canceled reservations. You will be able to see who canceled the reservation and when.
To "Restore" a canceled reservation, click the "..." and then "Restore Reservation". This will take you right to the modify reservation screen so you can verify the reservation information hasn't changed, and will be saved as active again. Please see the video below for an example of how to restore a canceled reservation.