Dear,
"Employment cancelled" as in Company broke? or Did the employer filled your position by someone else?
I would ask an immigration lawyer first if contacting any immigration authority would affect your status of permanent residence, because your whole immigration was based on the AEO. However what I know from the www.hrsdc.gc.ca is the following:
If the employer filled your position and there's no longer a vacancy for you, you should contact the officer who approved your AEO, you can find his/her contact information on the AEO approval letter that you first received from "Foreign Worker - Centre of Specialization". They sure can help you because by signing the AEO the employer has already agreed for hiring you and cannot withdraw whenever he/she likes.
Hope this helps.
Good luck