There are three must have books in my opinion. The Skeena River Journal, by Rob Brown, The Kispiox River Journal, by Art Lingren, and the Backroads Mapbook " Northern B.C., by Mussio Ventures. The Mapbook is sold in most gas stations up here now, and the other two books are published by Frank Amato and can be purchased or ordered through almost any flyshop.
Google Earth is a wonderful tool for some of the rivers, but others such as the Morice and Copper it is practically useless due to poor "graphics"
It's always well worth the $50 by stopping into a local flyshop, buying a few things, and asking some info.
The scenery is stunning, the people are warm and welcoming, and the fishing is second to none. You'll have a great trip, it's inevitable.