If you already have Canon lenses, stick with the Canon. Otherwise you may want to compare it with the Nikon d80. With both cameras, if you are serious, you are likely to end up spending more for lenses than you will for the camera body.
While the higher end Canons use a full 35 mm format for the sensor (meaning that lenses will give an image on the digital similar to what you get on the film camera), the Rebel uses a smaller format so that the "effective" focal length of your lens needs to be multiplied by 1.6 to to determine the comparable film lens. Thus, a 100 mm lens on the Rebel Digital results in an image comparable to what you would get with a 160 mm lens on the film camera. The same is true for the Nikons. This is good if you want to photograph retrievers in action since you can get away with a cheaper and lighter lens. The Canon is cheaper than the Nikon. It also has a narrower range of auto selectable "film" speeds (ISO 100-400 vs 100-1600). This could be important if you were likely to be taking shots in lower light situations. I shoot Nikons because I have a large investment in their lenses. Without that investment, it would be a toss up. You can generally get the best prices, widest selection, and best service from B&H at
http://www.bhphotovideo.com. It's a good web site for researching accessories and is used by many if not most professionals. I shoot with a Nikon D2X and love it but I would never have bought it if people weren't paying for my photos (It cost twice as much as my first new car).