Nice article, thanks for posting that Christian.
Robin, I posted earlier a picture of a knife I handled with birch bark from here in Wisconsin. Most birches that you have in Canada will have the same thickness of bark. I try to find a tree that has recently fallen or been cut to take the bark from. If you look for a tree that has been blown down or cut, you can experiment a little without worry of injuring a live tree. Aim to cut about 2 mm deep.
-Brian