Hi!
There is a full guide for visitor visas/supervisas on CIC website http://www.cic.gc.ca/english/visit/index.asp
You can also apply online http://www.cic.gc.ca/english/my_application/apply_online.asp You will need to pass online survey and based on the answers you gave, the system will show you the types of visa you (your parents) are eligible for. Documents checklist for your type of visa will be there too.