They didn't give any option to upload any other documents. When i started the application ,i didn't finish it in one turn. i saved it and went back to complete it. When i started the application ,there were lot of required documents that i can upload. But when i gave the UCI from my parents previous visa, the next time i logged in to complete the application, the list of supporting documents was short. I think the system already noticed that they come under CAN+.
Both parents passport pages(back page) has spouse name listed which means they are legally married. That would suffice the marriage certificate requirement.