A friend from work went out and bought that exact setup rip. It's a nice camera, but don't wast your money on the cheap 70-300mm lens. He was buying a new lens 3 months later. If you're going over 150mm in focal length, you're going to want stabilization control of some kind. For 300mm, you should be looking in the $700-$1400 price range. Especially if you plan on holding the camera by hand.
Also... the D20 is a bit better for sports. It can take pictures at 5 frames per second and has a 1600 iso setting for low light situations. The Nikon is better in situations that require a flash, but the Canon is definately better when you're not using a flash.