I am really very sorry to hear about your case. I suggest you to go for re-applying rather than appeal. Because if VO marked that your marriage in not valid under Hindu marriage act, that mean they had a solid evidence of that...coz VO think 100 times before rejecting a spousal case because they know if applicant win the appeal, it will raise a question upon them too, It is better if you get your marriage under a special marriage act because you are a Sikh and your wife is a Buddhist. did she batised to Buddhism or by birth ?
Secondly , if you will go for an appeal, and if you are landing in Ontario...IAD can take up 3 years for a final decision which is waste of time as well as money.
a question, if it is a first marriage of both of you? , arranged or Love?? ceremony was in India or abroad? all these factors are also important for a spousal sponsorship.
Good Luck you..