Here's a look at a canvas book I constructed during an in-person workshop with Kelly Kilmer several years ago. I thought I'd show it to you because it's one of my favorite books. Really delightful to hold. It measures 6-1/4" X 7-3/4". A pic would be better, but the lighting right now is awful, so I scanned it to get truer colors.
I painted the pages before binding the book. On the left is the inside cover with the first page on the right. The front cover actually folds over to create a pocket on the inside cover, which one of these days I'll probably stitch closed, top and bottom. The back cover does the same.
This is the whole book, flared-out butterfly style, with the back cover on the left, the spine in the middle, and the front cover on the right. Not a great scan because of the shadows on the left (the blurring is in the scan, not on the book), but this will give you an idea of how I created the spine by stenciling over the center of the canvas in black. It's sewn with a simple running stitch, one signature, pamphlet style.
I use a lot of canvas when I bind books, and I use it in many different ways. Here are a few links to other blog posts where I've used canvas in bookbinding:
I used painted and stenciled canvas to cover the boards for this book: http://artiphytheheart.typepad.com/artiphytheheart/2012/06/lateral-purple.html
I did the same thing here, except instead of stenciling by stippling paint, I slathered tinted modeling gel over the stencil to create the dimensional squares: http://artiphytheheart.typepad.com/artiphytheheart/2012/01/a-handbound-book-start-to-finish.html
I used painted canvas for the spine of this book: http://artiphytheheart.typepad.com/artiphytheheart/2011/07/my-18x-book.html