I want to use for both portraits (babies) and equine photography (speed events)

If you're willing to put in the money to buy new lenses, the Nikon's the best bet. Nikon lenses often get better performance scores on dxomark tests, which means they give sharper and higher quality images with less drawbacks like chromatic abberation or vignetting.. Plus the D7000 has both lower noise at high ISO (perfect for your dark situations) and better colour depth which will make a massive difference in portraits.

I personally feel d7000 as is very suitable for low light n excellent image quality

If you are already a canon user, stick with the Canon 7d - there's not enough difference in these two cameras to justify switching brands.  The best option for you is to invest a bit more money in fast primes for shooting in the dark areas, then bump your ISO up to between 400-800 and shoot at low aperture.  Most 1.8 primes are relatively cheap and will give you 2-3 stops of light.  Dont keep the lens at 1.8 at all times or you will have too shallow DOF, shoot around 2.8-4 for best results.

Then, when you are shooting outside in a well lit area, you can slap on a zoom lens for more versatility.

The recommendation is not that hard, the 7D Autofocus has it's own processor, it's extremly fast and reliable.  The shutter is fast, 12 fps, enough to get it all.

The fact that it is a crop camera means you get that extra millimeter for free. Unbeatable in combination with an ef 300/400/600 for sports and action.

i was once leaning towards 7d but the following criteria made me decided over the nikon D7000:

1. shutter button is bigger (you wouldn't get firing the wrong button when in the dark)

2. the grip suits my hands (i have big hands, i love the way my lower 3 fingers grip the body, my pointing finger on the shutter and my thumb pressing near the lcd)

3. the User Interface is not hard to understand. (there's (?) button which helps me to understand what this function do to my camera)

4. i barely shoot videos (if ever i do, i only do it on my child so i don't need a high end video capable camera)

5. budget and flexibility in upgrading (well, this one is my opinion)

Nikon D7000 is a lot better when came to performance and quality. I have a Nikon D7000 and I've been using it already for a year and never let me down. One thing that a D7000 has is when it cames to picture quality. Its alot more better colors and depth than the 7D. And also let's talk about the pricing. I know you would like to save money and have a better camera. So I would let you know that the D7000 will really help you in your needs just like what it does to me. :)

As you do have Canon lenses, you should go with a Canon.

1) Try using a huge ISO. As it is a bad spot to do photography, some noise can be negligible!

Generally, the newer the camera, the better the ISO performance (less noise)

2) Shoot in RAW!!! You can use Lightroom to boost your exposure up to 5 stops, but from experience +2 is the limit when it comes to noise.

3) You might like primes. They tend to offer f/1.8 at a ok price (even f/1.4 if you have the extra $$$)

The problem is that your DoF will be hard to manage! A good Auto Focus will be your only friend!

I know the feeling of not having enough light... Hope you get to manage!

I use the D7000 indoors with a 35mm 1.8 lens w/o flash, with no problems. I guess if you already have a fast Canon lens you could stick to the Canon system, since its a great camera as well. Im just saying that Im pleased with my D7000 and I recommend it. Hope this helps.

I'd say 6D since you have a lot of Canon glass, but beware, that's a full-frame camera and some glass you have might be suitable only for APS-C sensors. If you don't have any full-frame lens, you can also consider switching to Nikon (D600) instead.

Get the D7000 its cheaper and the Sensor is the newest Sony co-production model wich means that is the best 16MP sensor on the market i think.

In many ways these two cameras are similar but the Nikon has a slight advantage with low light over the Canon. I don't want to get too technical but with the Nikon you get more focus points 39 compared to 19 on the Canon. Both have the same ISO range 100 to 6400 but the Nikon with boost is 25600 useful in low light. The only trade off on this is the Canon has slightly better resolution and 17.9 MP.

I do own both Canon and Nikon cameras but in this case the Nikon is a better buy.  

among these two, for your requirement surely EOS 7D. but if you want nikon one for your lenses if already you have, then D800. which is very costlier but very good in low light conditions!...

More cross sensors and nikon menu is boring