This is what is available for a cancel event. Taken from:
https://freeswitch.org/confluence/display/FREESWITCH/mod_callcenter#EVENTS
Event-Subclass: callcenter::info
Event-Name: CUSTOM
CC-Queue: support@default
CC-Action: member-queue-end
CC-Member-Joined-Time: 9000
CC-Member-Leaving-Time: 10050
CC-Cause: Cancel
CC-Cancel-Reason: TIMEOUT
CC-Member-UUID: 453324f8-3424-4322-4242362fd23d
CC-Member-Session-UUID: e260ffd0-a731-11df-9341-e7d9456f8886
CC-Member-CID-Name: Marc O Robinson
CC-Member-CID-Number: 5145551212