It's a bit of a toss up... Will depend mostly upon your uses. I use a pair of 7Ds complemented with a 5DII.
7D is a better "sports/action" camera.
Thanks to being full frame, the 6D is better for really big enlargements (say over 16x24") and for low light shooting without flash. You really have to make big enlargements to take full advantage of the additional fine detail that FF is capable of. If all you do with your images is post online and make 5x7 and 8x10 prints, you won't really see the full benefit of FF. The far less crowded FF sensor also allows 2 or 3 stops higher ISO be used before image noise becomes an issue (Say, for example, if you use 7D up to 3200 now, you might be able to get similar results at 12800 with 6D). Sure, 6D is able to shoot action, but largely will be limited to the center AF point only and simply won't give you as many "keepers" as 7D would in the same situation.
7D's AF is optimized to track movement (using a discrete chip to drive AF, 1D series style) and has a much higher frame rate. 6D is not, though it's better at it than 5DII and 5D classic.
For travel, 6D is slightly smaller and lighter. However, what you gain there is more than offset by being limited to "full frame capable" lenses, which on the whole tend to be larger, heavier and more expensive. There's some, but not a lot of difference at the wide end... for example compare the size, weight and price of EF-S 10-22mm for use on 7D with EF 17-40/4L for use on 6D. The biggest differences are seen at the telephoto end. You have a 70-300 now, and to enjoy the same "effective reach" on 6D would need to invest in a lens that reaches 500mm (well, actually 480mm). That will be a much larger, heavier and - typically - more expensive lens. Of course, for portraiture and travel, you might not need nearly as long a lens as you did with equestrian photography.
I use my 7Ds for sports/action (including a lot of equestrian photography). Probably 85 or 90% of my shooting is done with those crop cameras, because it's the bulk of my work. The remainder - particularly portraits, landscape/scenic, some macro, and low light - I prefer to use the 5DII (6D would be very similar).
6D has a far simpler AF system than 7D. 11 points, only the center one is the "better" dual axis/cross type. It's able to focus to -3EV (moonlight) at center point only, while 7D gives up focusing at about -1EV light level. It's low light AF performance complements the 6D's cleaner high ISO image capabilities nicely.
Ultimately, 7D can be used for portraits and travel.... it's just sort of a waste, since it's optimized for sports/action, to not use it for those purposes. 6D, on the other hand, is more ideal for portraits and scenic shots, also can manage some action photography (again, better than the 5D or 5DII), but will never be as good at it as the 7D.
Glass might be an important consideration, if you plan to upgrade there. Actually, better glass might be the best use of your money. There are some excellent lenses for both crop cameras and full frame (some of which are largely exclusive to one or the other). I might let that be a key determining factor (in addition to planned uses)... looking at the cost of lens upgrades for each format, then consider whether it's in the budget or not.
For example, EF-S 10-22mm, EF-S 15-85mm, EF 70-300 "DO" lenses make for a pretty neat and reasonably compact travel kit with 7D. Maybe a couple fast primes, too... such as EF 28/1.8, or 24/2.8 IS and 50/1.4.
Meanwhile, for 6D you might look at 17-40/4L, 24-70/4L IS or 24-105L (IMO, the far less expensive 28-135 IS can serve nearly as well, can't tell the difference in images), and 70-300 "DO" or 100-400L, or Sigma 150-500mm OS ("BIgma"), depending upon how much you want to haul around. Maybe 35/2 IS or 50/1.4 and 85/1.8 primes, too. The 135/2L is a fabulous portrait lens on a full frame camera, too.
By the way, with 6D you'd need to get new memory cards, too. It uses SD, not the Compactflash cards your 7D uses. Also, what softwares do you use? 6D and some other recent camera models are incompatible with some older versions of Adobe products, for example. You might need a s'ware upgrade too, and that can add significant cost. (When I upgraded from 30D to 50D, that meant a Photoshop upgrade, which in turn meant an operating system upgrade, and ultimately ended up being a complete desktop and laptop computer upgrade! Far more than "just a camera upgrade"!)