I am a US Citizen, but have Canadian citizen...need help

Hello Everyone,
I am a US citizen. When I was 14 years old, my mom remarried to to a Canadian citizen. At that time they took my brother and I to somewhere downtown of Alberta to get the Canadian green card...after living in Calgary for 6 years, my mother, brother, and I went back to California, and live here ever since. while we left Canada, the Canadian guy that married my mother destroyed all of our Canadian legal paper. At that time, it didn't bother us, because we still had our US passport to go back to the states.
SO after living in the states for the last 7 years, now my mom, brother, and I want to relocate to Vancouver, B.C, but We do not remember nor have any of our legal numbers, or Canadian green card.

NOW MY QUESTION IS:
1) HOW could my family could obtain these Canadian paper back, since my mom's Ex-husband is dead 5 years ago in a car accident
2) Who, where should I call to find more information about obtain the replacement documents without know these numbers.
3) Can any Canadian immigration attorney or private investigator find these out for me.

millions thanks to all comments.

Zetia

Not sure that you are Cdn citizen. If you were merely Cdn permanent residwent and never applied for Cdn citizenship, you are not likley Cdn.