Hi,
The first thing you need to decide is whether you want to go with a full frame camera or stick with a crop camera. There are advantages to both... but essentially you'd be able to use your 50mm lens on FF, but that's about it. You'd have to replace your 17-55 (24-70 is the closest equivalent) and FF lenses will tend to be bigger, heavier and more expensive. Plus you have less lens selection, since crop cameras can use both EF and EF-S lenses, while FF can only use EF.
FF... only the 1Ds, 1DX and 5D Mark III offer 100% viewfinder. 5D Mark II is close, though... 98%.
7D is the only crop Canon offering 100% viewfinder. 60D is 96%, 50D is 95% which is the same as your T2i. The 1D series, 5D series, 7D and xxD series cameras all use a true pentaprism, which makes their viewfinders a little brighter and feel a little larger... the xxxD/Rebel series like your T2i use a penta-mirror, which is lighter, smaller and less expensive.
100% viewfinder is not necessarily all that big a deal. In fact, you have to be careful... there's a little "fudge factor" at the edges with a less than 100% VF... none when it's truly 100%. I have to watch that I don't crop too tightly, using cameras with 100 and 98% viewfinders.
Brightness and size of the display are usually more critical... and 60D on up would all offer that, compared to your camera.
Also, the focus systems on all of them from T4i on up are a bit or a lot improved.... except for the 5D/5DII, which are more similar to your camera.
Sorry... but the above is incorrect.... Image quality and high ISO performance of 60D, 7D, T4i are nearly identical to T2i and T3i. They all use a very similar 18MP sensor... and they all process images through a Digic 4 processor (two processors in the 7D to support 8 frames per second shooting), except for the T4i which uses a newer Digic 5 processor. Don't expect much difference in IQ or high ISO performance, unless you go to a FF 5DII or 5DIII. For what you shoot, 5DII would probably be just fine. 5DIII is an important upgrade... but the bulk of it is in the much improved AF system, that would be most useful if shooting moving subjects... sports/birds/wildlife, for example. And it's $1300-$1500 more expensive. Only you can say if it's worth that much to you, for your purposes.
Unless you print really large, you won't really see the additional fine detail the full frame cameras capture. However they are good for about one stop higher ISO, have slightly greater dynamic range (retaining a little more detail in shadows and highlights), and render slightler smoother tonal gradations. Full frame also offers a bit more control over depth of field, in part because it's easier to see what you are getting, on the larger format. DOF actually doesn't change with the change in format, however using the same focal length on both formats, you have to move closer if you want to maintain the same framing, which gives shallower depth of field at the same aperture. Alternatively, you can use a longer focal length on the FF camera to maintain the same framing, which also renders a shallower DOF. At the other end of the spectrum, the full frame sensor is less "crowded" with pixel sites, so it's a little less prone to diffraction effects... so you can use a little smaller apertures, too.
Of course, there are also price differences, between crop and full frame cameras.
Okay... once you decide on the format, you can start thinking about lenses. If you stick with crop cameras, you can keep using your 17-55, which is an excellent lens in many ways. Complement it with a wider lens (Tokina 11-16/2.8 or Sigma 8-16 would be a couple options... there are many others).
Also the 17-55 would match up quite well with the 70-200 of your choosing. I'd recommend an IS lens, to help with handholding it... then it's just a matter of the more compact f4 or the larger f2.8. Canon's 70-200s are hard to beat!
If you opt instead for a FF camera, you'll need to replace the 17-55... the most direct replacement option is the 24-70/2.8.
And, with FF, your 50mm will work just fine, but it will no longer be a "short/portrait telephoto" that it acts as on your current crop camera. So you might want to budget to add an 85/1.8 or the Sigma 85/1.4, at least.
70-200 will also work quite well on FF... but will give less "reach". You'd need to add at least a 300mm as well, if you use the longer end of the 200mm on crop now. Or, you might get an 1.4X teleconverter (can't really use a 2X on an f4 lens, you lose AF). Of course, there are other options... such as the 100-400 or Sigma 120-400.
But, decide on your camera first... then that will guide you toward what lenses you need.