The only lens that I currently have is the 70-200 f/2.8 IS
*Eyebrow Raise* That's a new one... How did you end up with a $2500 lens as your ONLY one?
Kinda like "my first apartment ever was a penthouse loft on the upper west side of Manhattan" or something.
ANYWAY
Your two stated types of photography are sort of at cross-purposes in terms of an upgrade.
For the horse stuff, the 7D makes a lot of sense. It's pretty clearly designed as an action camera, and all of the features you'd gain would be useful for horses.
For the portraiture, though, a 7D is a clumsy choice. A full frame camera would be more ideal, largely for its shallower depth of field that it inherently brings to the table (also better able to deal with various lighting situations without restricting you), and the
6D is in the same price range as the 7D. 6Ds are probably not as good for action, though, since it is slower in FPS and I think it has a worse AF points system, and it makes your lens appear wider (without having the same pixel depth to compensate if you crop later on).
I don't know what to recommend. It depends on where more of your future plans lie.
Also, as mentioned, for portrait work, it would probably be more efficient to upgrade your lens "collection" than a new body, for now. Having something on hand wider than 70, and having some brighter apertures than 2.8. Although the 70-200 2.8 is a great portrait lens for certain types of shots, no doubt, the relative advantage of a couple fast wider primes is greater than a new body there.