I have a backroads book for BC if you want to borrow it. I fish BC quite often. Based upon my experiences have to use various maps like the backroads books, join internet BC fishing forums and talk to locals up there in fly shops and on the water and get out and fish and take notes.
I have yet to find one good source of fly fishing info for BC.
Not sure how Canada does their census. They might not do a map set to check for residents.
Also as I understand it the Canadian government "sells" their data, whereas, all the US Government maps are in public domain. The US Government could do pretty well selling GPS access, maps, and other stuff that is free!!