Right now canon feels a bit lackluster compared to Nikon with its new DSLR's (especially on the full-frame segment, my fiance bought a Nikon D800 recently and is just out performs the Mark3 while it is cheaper*)
Watch out for bad karma flying in your direction, this is a Canon enthusiast's forum :-p ... really, d800 & 5d3 have different usage scenarios: high-mp landscape vs higher iso event/wedding, but of course you can use them vice versa, too. But personally, I also think that the 5d3 is currently overpriced and will drop a lot after pros & well-off early adopters got theirs.
I've read about the full frame discussion if the 7D2 will be a full frame yes or no, and honestly I can't really decide if I'd like a FF yes or no.
If you're asking this question chances are you don't need a ff sensor - there are only specific scenarios when the current aps-c sensor is too limited, though they matter a lot to many.
Don't get me wrong here, I picked canon over Nikon at the time, even bearing in mind I wouldn't be able to share lenses with my fiance (Boyfriend back then =P ) and I'm strictly speaking about the mark3 and D800. I've always had a weakness for canon (not just camera's) for some reason I just like their products, I'm just a bit disappointed with the price/performance difference on both camera's. (also thanks for explaining the different usage scenario's - didn't realize that! see, I have a lot to learn
About the full frame, I just started shooting in November 2011, got my T3i in December so I'm just afraid that in the future I will want FF. That's why I'm unsure right now
I don't have that much experience yet, I shoot a few nice macro's but for now that's about it. I might want to look into studio and wedding photography later so I'm really scratching behind my ears as in 'what to do?' I don't want to spend a bunch of money on a camera only to realize later I'd rather have FF (or not ..