Yakima Racks makes a very sweet setup for exactly the application you are talking about. You'll first off use the Yakima Q Tower Half Pack roof rack on the cab roof top. It includes a pair of Yakima Q118 clips (these Yakima Q Clips are specific to your 2008 Chevy Silverado), two upright Yakima Q Towers and a single cross bar. This will be the front cross bar that you will connect the canoe carrier to. The 58 inch crossbar is the recommended length for your pickup.
You'll then want to attach the Yakima DryDock t-bar rack to the rear trailer hitch receiver. You will attach the canoe carrier to this as well. Note that you will need to also get a single cross bar to work in combination with the DryDock. Just get the same length crossbar as you are using on the Yakima Q Tower Half Pack system (normally a 58 inch crossbar).
Then get the Yakima Gunwale Brackets Canoe Carrier. The Gunwale Brackets connect to the crossbars. This canoe rack also includes straps to tie down the canoe so you don't have to worry about getting extra straps or anything.
Here's an example picture of the Yakima Q Tower Half Pack and DryDock installed on a pickup truck...
http://www.orsracksdirect.com/ford-f250-yakima-q-towers-half-pack-drydock.html