Were you adopted as well, or do you know the names of your birth parents? Have you contacted the adoption registrar to see if you can get info such as the adoption agency involved? they told me which agency I was adopted from by giving them very basic information (the names of my adoptive parents, name of hospital, date of birth).
You might be entitled to non-identifying information and there is a sample letter you can follow on
http://www.canadianadopteesregistry.org
You should also register at that site as the sibling looking for an adoptee - they can post your listing under both years since you are unsure of the year of birth.