As I understand it's not a must to hold Canadian passport for application. Anyway, they don't interview all candidates. If you hold a Canadian passport, they will offer you a interview.
Not a must to have a passport. Only a fare percentage of kids are holding Canadian passport. You don't have to buy a debenture and you are only allowed to buy one after you have an offer.
AISHK is doing a better job than CDNIS on this passport aspect, CDNIS now is more diversify while AISHK is focusing on giving spots to Aussie an Kiwi...