Hi
Is your friend a landed immigrant? Or he still has his permanent residency application on process? If he's a PR already, or if he landed recently, he could send back the docs to CIC to change the marital status with proof of marriage and a letter explaining why he didn't do so when landed. If his PR is on process, call CIC or send them a letter to update his marital status asap. He can either add his spouse in the application or just pass it and apply her later when he got his PR
(--- advises from experts when I got my sponsorship refused, same mistake as his. I was categorized as mispresentation ---)
Once you "land" and declare yourself as single, that it is it, there is no going back to CIC, and it is misrepresentation.
PMM