The right to freedom of speech is not unlimited in Canada. It's specified in section 2b of the Canadian Charter of Rights and Freedoms as "freedom of thought, belief, opinion and expression, including freedom of the press and other media of communication;" but section 1 of the Charter says, "The Canadian Charter of Rights and Freedoms guarantees the rights and freedoms set out in it subject only to such reasonable limits prescribed by law as can be demonstrably justified in a free and democratic society." Plus, that only affects the government's ability to curtail your freedom of speech.

In any case, the Ontario College of Psychologists is not a government body, but a professional college. This guy behaved unprofessionally, and therefore is a reasonable target for professional sanctions. Since words are one of a psychologist's instruments for treating (mental) illnesses, what he's done is pretty damned close to a regular physician who's approached by someone at a party suggesting they take a drug that they know won't treat the illness and has nasty and occasionally fatal side effects (rather than just telling them to go away). Technically that person is not their patient, but they still have a minimal duty of care not to give advice that they know to be actively harmful.

He can have either the freedom to be verbally abusive in public or retain his license to practice psychology. I don't think it's unreasonable to ask him to find a new job if his current one asks more of him than he wants to give.