Going to Canada in June and have been researching a few things myself. I do recall seeing duty fees posted on the Canada Border Services Patrol website. Don't recall how I got to it, but here's the link to their site:
http://cbsa-asfc.gc.ca/menu-eng.html
I would use their "Search" link near the top of their home page and try searching on "duty fees", "Liquor", etc.... It's out there. Good luck and have a safe trip