There are a lot of hoops to jump through but its fairly easy. I would recommend buying an existing spa. Building one is a pain.
Jamiewolf is incorrect about the city of toronto and licencing. There is no such thing as a "spa transfer" there are considered a new business each time even in the same location. They are issuing licences for new spa business.
You can do some general easy math, Owner makes $30 per client and 10 clients per day x 30 days. less rent and expenses