Hi,
91 %!! That's impressive. You are likely to be India's next Nobel Prize winner for either Physics or Chemistry
But why Diploma? Why not a full undergraduate degree? Since you have already been rejected with your first visa application, so it's time to be extremely careful for your next possible attempt. It's clearly written that a rejected applicant can apply if there is any “significant change” in his papers. So, tell me what's the significant change on your part?
Just think, even VO did not care about your hard earned 91 % and simply rejected your candidature. I would strongly suggest you to go for a full Undergraduate degree. Rejection rate is VERY HIGH for a Diploma/Certificate Course. Rest is your choice!
Fees requirement is almost same. I mean you have to show 80 percent of first year tuition fees + living expenses (CAD 8,000), applicable in INDIA only.