I had this lens when I shot Nikon, and it was awesome. Sigma makes both Gems and Dogs, and this one is a Gem. I shot wit the Sigma 1.4X and loved it for sports, wide life, etc.
A Canon f2.8 IS II would also be nice, but we would all think you were stuck up and pretentious. (Kidding) It's a better lens for Waaaay more money. Consider the IS I, or pre IS 300mm Canons as well.