Bank drafts must be less then 3 months. Beyond 3 months, you can easily go to your bank and ask that they process a new one. I know someone in this forum, ittech, whose application was sent on 24/05/2011 and recd the next day. He just recd his application back because of some incomplete info. The draft wasnt cashed either for that reason.
So, my advice is wait a little longer till about 3 mths and one week or even 3mths and 2 weeks and contact Buffalo to say you will cancel the draft and do a new one and know how to have it link to your file. Then cancel or BD and get another one.
Basically wait another month just to be safe and know :
For files that are complete, Buffalo will accepts Bank draft, Money order, Cashier's cheque when made payable to the Consulate General of Canada. These financial instruments have a limited validity. Ensure that the instrument is not older than3 months when it reaches our office.
Retrieved from: http://www.canadainternational.gc.ca/buffalo/assets/pdfs/visas/50_1_eng.pdf