Visitor Insurance is for those that are visiting Canada from abroad. SuperVisa is type of Visitor Insurance, except that it is desgined only for parents and grandparents that are being sponsored through the SuperVisa program.
Visitor Insurance is typically for 90 days, although can be for any period of time, from 1 day upto 1 year
SuperVisa Insurance is a 1-year policy that is mandatory to have in order to apply for the SuperVisa program. Thus, if any medical emergency were to come up it can get expensive.
Travel Insurance on the other-hand is for Canadians and Permanent Residents of Canada that are traveling outside of Canada, and looking for coverage to protect them while away from the country.