Stick with the T2i. I have a T3i and my dad has a 7D, if I had the chance to upgrade or even have his, I wouldn't. They're essentially capable of all the same things at an equal caliber.
You'll think that 8fps and weather sealing are a selling point for the 7D right now but honestly it's not THAT worth it. I take a ton of pictures and video with my T3i and rarely feel limited by it.
As for your lens choices, I haven't done any research on the Sigma, but it seems like a classic "sellout" lens; something that is built for people who think they can cut the corners of needing a medium zoom lens and a long zoom lens. It's probably not built extremely well.
Thus, I'd urge the classic NS setup. It seems so cliche that the same setup is recommended all over this site, but it's recommended because it's so good.
First I'd recommend buying a Tamron 17-50 2.8 non-VC
After that, a Tokina 11-16 - Don't get the Rokinon 8mm. My friend has had both lenses and he regrets having the 8mm because it's not very sharp (especially at 3.5) and the distortion isn't as worth it. It'll cost more but it will be a better investment.
After that, look at any of the 70-200 line by Canon, those are some incredible lenses.
Cheers!