I'm going to correct you. The exemption applies across Canada for both the GST and the HST. Maybe I can explain why there's confusion here.
There are administrative criteria that are used to decide which health care professions would benefit from the exemption, and one of those criteria is that the profession is regulated as a health care profession in at least five provinces. When that criteria is met, usually an association will make representations to the government asking to be exempt, and then a decision to exempt will be made by the minister. Once it's exempt, it's exempt across Canada.