Suggest me which SLR should i buy?

12mpx sensor may handle noise better while 22 mpx may give u image resolution more over a bit less advantage on noise

check the nikon d800 or wait for a bit cheaper d600

You can get a D700 used for about 1800 or get the new D600 for 2200. Not sure if the D600 does better in high iso than the D700 but I know the 700 which I have is insanely awesome.

Also the D600 shoots video.. so its like a bonus if you ever did want to mess around with video.

How expensive are your canon lenses? Are they fixed aperture lenses and are they full frame?

if they are not full frame lenses then that makes the switch easier.. and same if they are just cheap lenses. I only buy full frame lenses with a fixed fstop under 3. My highest fstop is 2.8 all are fixed and full frame.

If you switch to nikon you will have to sell all your gear and replace it with nikon stuff. Sure you can get an adaptor to go from canon to nikon lens.. but in my opinion the nikon lenses are a better build. Canon lenses and bodies feel like cheap plastic.

If you are not into sports and action photography (ex. hockey: a fast sport in a low lit environment) you would very well served with the 6D,  It has amazing low light capabilities.  Actually, it has very similar capabilities to the 5D mark iii except for the single cross-point AF.  For portrait, landscape and macro, it isn't a problem, for sports photography, it would be.  The 6D is a natural step-up from your 7D,

Because its the best you can find out there for that price

I've seen some sample photos and videos and i'm speechless. Great skin tones, Hi-ISO behaviour is amazing. Price is also a plus.

u got the canon 7d and canon 600d . im sure u have some prime lens that could be use with a full frame canon camera .. so grab that canon 5d markiii.. price is falling .on  ebay u can get one for like 2990-3200 usd!!.besides canon 7d and 5d mark iii share the same batteries .

Able to use your current glass