The Canon EF 70-300mm f/4-5.6L IS USM lens is one of my favorite lenses, but I personally would not pair it with a Rebel. I use to own a Rebel xti as a backup camera and I found that the heavier L lenses did not balance well with the lighter weight Rebel bodies. This can cause a tripod setup to accidentally tip over and damage your expensive lens. And even handheld, it just feels front heavy and sort of awkward, whereas it balances perfectly on the Canon 5D Mark II or the Canon 7D. Additionally, this lens is designed to give exceptional autofocus tracking with a high performance tracking system such as the one introduced on the Canon 7D and the improved versions on some subsequent models. I believe the Rebels still have a 9 point, less sophisticated system, so I'm not sure you would really get the full benefit of the len's capabilities.
Have you considered the Canon 70-300mm lens that lists for about $650.00. I've read excellent reviews on this lens and I think it would pair better with your camera. Please understand, I'm not knocking the Rebel line. They are fine consumer grade cameras with tons of features, but not necessarily the features needed to see the true benefit of this L lens.
Thank you for your honest insight and opinion. I am leaning on getting the the lens using it with my Rebel with the intention of upgrading to the 7D. I've had my Rebel for about 6 years now, and am ready to upgrade to a semi pro lens