A school principal, doctor, minister, professional engineer (not sure if a CGA can do it or not)....They must have known you for a certain amount of time (2 years?) and not be immediate family.
Found this list online from the Canadian passport site:
Chiropractor
Dentist
Geoscientist
Judge
Lawyer (member of a provincial bar association), notary in Quebec
Magistrate
Mayor
Medical doctor
Minister of religion authorized under provincial law to perform marriages
Notary public
Optometrist
Pharmacist
Police officer (municipal, provincial or RCMP)
Postmaster
Principal of a primary or secondary school
Professional accountant (APA, CA, CGA, CMA, PA, RPA)
Professional engineer (P.Eng., Eng. in Quebec)
Senior administrator in a community college (includes CEGEPs)
Senior administrator or teacher in a university
Veterinarian