What I would like to stress however, is there is nothing stoping any MD from practicing Psychiatry. Technically an MD needn't qualify with any body to practice any sort of allopathic medicine. i.e. A newly graduated MD with a GP residence can start to do heart surgery, poediatry, plastic surgery, psychiatry, dermatology... etc... However, to be taken seriously in any of those disceplines one should certify with the appropriate body. So, the minimum to become a psychiatrist in Canada:
3 years of undergrad (pass degree) with appropriate scores in Chem (reg,org,inorg), calculus (Not always required), physics, and English.
Pass the MCAT examination with a reasonable score (Not required for all med schools, i.e. McMaster)
4 years of general medical training. including clinical (i.e. working in a hospital)
<you're now a "student doctor", not an MD>
At which time you hope that a "teaching hospital" will have a person in the discipline you'd like to pursue will take you under his/her wing.
You'd then complete 2-4 years of residence training, still as a "student doctor" until the mentor physician decides you know enough to become a "staff <whatever>". The mentor will then relay this information to your med institution.
<you're now an MD, and are free to practice whatever your little heart desires. You'd be best to practice the discipline practiced in your residence>
you can then choose whether or not to certify with the appropriate body. (APA / CPA) Should you not decide to certify, it will be difficult to develop a patient base, as hospitals would never hire a non-APA/CPA psychiatrist, nor would a GP refer a patient to you.
cheers!
Trevor