1) Kelvin Temp white balance. Rebels don't have this.
2) The ISO increments in 1/3 stops allow you to use SIO speeds of 160, 320, 640, 1250, 2500... these ISO values have lower noise.
3) Better battery. very much needed when shooting all day (like at weddings). Don't get me wrong, you still have tobring extra batteries and swap out... but oinly about half as often
4) the T4i AF is cool if you just anna leave it on a tripod and forget about it (as a second angle) but you'll probably want to invest in a decent follow focus and focus manually anyway. It's funner. It looks better/smoother.
As far as lenses, I wouldn't rec the 24-105. At f/4, it's just so so. Go primes when shooting video. You'll like having the really shallow DOF to play with. I got my 35L specifically for video use (although i do use it for stills a lot too). That and the 50 f/1.4 work nicely. The 70-200 looks nice too. At the very least, get an f/2.8 lens like the 24-70 vI or II, or the 40mm f/2.8. As far as IS, I'd prefer a good video monopod any day over trying to rely on a lens's image stabilization.