The Nikon vs. Canon thing is more of a religious debate and it's not unlike asking which beer you drink and whether you drive a Ford vs. a Chevy. Frankly they're ALL great. You can find individual nuances where one camera will seem better, but you'll find some other feature where the other camera is better. As far as the basic foundational features and performance are concerned, they're all great.
This might provoke the question: if they're all great, then why are there so many choices?
There are lots of little feature differences between the models even though the core features are the same across products.
For example... Canon releases a new "Rebel" model nearly every year. The T4i is "this years" latest model. T he "T3i" was "last years" new latest model. The T3i introduced a rear LCD that swings out and swivels (great when you're shooting from odd angles and can't stand behind the camera) The T2i didn't have that (the LCD was flat the back and didn't hinge out). The T4i adds a touch-screen LCD on the back. While the T3i can trigger a remote speedlite (flash) using IR, the T4i can trigger a remote light using radio triggering (which is new).
A fairly big feature of the T4i is that it's 9 point auto-focus system now uses all "cross type" focus points. In prior models you had 9 points, but only the "center" point was cross type. The other 8 points only check focus on one axis. It's possible to fool a single-axis focus system with some subjects. A focus system needs to find some contrast and usually that contrast will appear at the "edge" of a subject. If those edges are in the same direction as the focus system axis (rather than cutting across the axis) then the camera might not detect the focus accurately. When the focus points detect focus along two perpendicular axes simultaneously then the direction of the edge of a subject wont matter... the focus point will always find focus and it'll do so both faster and more accurately. PREVIOUSLY in order to get more than 1 cross-type auto-focus point you had to upgrade to a Canon 60D or higher model.
The 60D is a "pro-sumer" body (a mid-range body rather than an entry-level body such as the Rebel line). It has all 9 cross-type AF points, a swing-out LCD (but it's not touch-sensitive like the T4i because the 60D was released a couple of years ago). The body grips are better. Rather than a single selection wheel the 60D has two... one in front and one in back. This is really nice for photographers who shoot in manual mode. On a Rebel (which only has a front wheel located just behind the shutter button) you can use the wheel to change shutter speed in shutter priority mode or f-stop in aperture priority mode. But in "manual" mode it'll normally control shutter speed and you have to press and hold an extra button while adjusting the wheel to control f-stop. You get used to this operation but on a 60D the controls are laid out more like Canon's higher end bodies (the 7D, 5D, and 1D series bodies). The front wheel does shutter speed and the rear wheel (which you turn with your thumb) handles aperture. The 60D is "weather sealed" which means it has gaskets on all body seams and buttons and the dials have o-rings to keep out moisture and dust. This doesn't make it "water proof" (if you submerge it underwater it will flood) but it does make it weather resistant (if it rains you wont need to worry that the water will get into the camera. Nothing will get in unless it's under pressure.)
The 7D is optimized for action / sports shooting. It has DUAL processors. It uses CF memory cards rather than SD cards (CF cards are larger but have a much faster data transfer speed). It can burst shots at 8 frames per second in "continuous" mode. Rather than a 9-point autofocus system, it has a 19 point auto-focus system and ALL 19 points are "cross type". It also has a magnesium alloy body (metal) rather than a polycarbonate (plastic) body. Like the 60D it is also weather sealed.
All of these cameras have Canon's 18MP APS-C size sensor (although due to tiny differences in the processors and firmware the image quality is fractionally different... but not so you'd notice. Effectively they're all the same when it comes to core functionality and image quality. Image quality is mostly influenced by lenses.
Then there's the 5D bodies... the MAIN difference with the 5D bodies is that they have "full frame" sensors. All Rebels, the 60D and the 7D bodies have "APS-C" size sensors. These are a little over 1/3rd smaller than the sensor on a 5D. The 5D sensor is the same size as a 35mm film negative. The 5D bodies are extremely popular among wedding & landscape photographers but not sports photographers. That's mostly because the bodies optimized for sports (the 7D, 1D IV and now the new 1D X) are blazingly fast but the 5D bodies aren't optimized for speed. The 5D II body only has a single cross-type AF point and the rest are single-axis only. The new 5D III has the same AF system as the 1D X -- a 61 point AF array and 41 of those points are "cross type". While the 5D III isn't quite as fast as the 7D in burst speed, it's much better than most cameras.
HOWEVER... for your purposes (shots of horses and landscapes) frankly any DSLR will do quite nicely.
The Rebel bodies are, in fact, quite high quality and extremely durable. All DSLR bodies from Canon or Nikon are actually quite good. The Rebel bodies aren't weather sealed but the polycarbonate bodies are quite solid. These bodies can take a fair beating and nothing other than scuff marks to show for it. Don't be afraid to put your camera to work. You don't have to handle it with kid-gloves. It can take it.