Get the Rebel. They're some who will say that neither camera is suitable for shooting weddings. But if you're serious and don't want to miss any shots. Get the rebel. If you can afford it get the 420ex flash too.
Before I realized how serious wedding photography was, I actually entertained the idea of shooting a wedding with my Nikon 5000 digicam. I now have a Canon 10D and I consider it the minmum quality camera that I would use in shooting weddings. Another thing, get at least two 512mb compact flash cards. Don'tusea single1Gb card because you need redundancy if one card fails. Shoot any tricky lighted scenes using the raw mode. GOOD LUCK!