Bi-curious about canon...
There are many posts comparing the two systems. It comes down to personal preference. There are pros and cons to both. I personally prefer the Canon ergonomics and menu system. I believe Canon has a better and more versatile lens line up that isn't confusing like Nikon's.
The D700 is a great camera, as is the D800. You are likely to get more out of practice and lenses/accessories than you will by changing systems.
That said, Canon's 5D Mark III is more versatile than the D800 from a "get the shot" perspective. The D800 is more versatile in post with it's increased dynamic range and increased resolution.
I would favor the 5D3 for event/photojournalists and photo enthusiasts. I would favor the D800 for studio work or for those that need to print billboards/murals.