Ignoring all the various opinions regarding what camera body, I think it's actually more important to think about lenses. For portraiture, obviously the old favourites such as 85, 105 and 135mm will be popular, but if you do need something more 'versatile', then I would really recommend a 70-200mm f2.8. Don't know anything about the Canon versions, other than they are reputedly excellent. Big and heavy though, if compared to most primes. And seemingly a lot better value for money, given their versatility (plus they have built in VR), whereas most primes don't, not in DSLR format anyway. F2.8 is plenty large enough for most portraiture, where You want sufficient depth of field to get eyes and noses etc in focus, but with enough control over DoF to isolate the subject. I have a Nikon 70-200mm lens, and it's absolutely fantastic.
But then.
The thing about yer primes, is that they offer some benefits that a lot of portrait photographers consider very important, if not essential. That larger maximum aperture for example, with f1.8 and f1.4 lenses (even up to f1.2 with Canon!), allows even more control over DoF and subject isolation. A prime, especially a f1.8 version such as an 85mm, will be significantly smaller and lighter, and potentially less intimidating for subjects; I've noticed people being a bit uneasy when I've pointed my 70-200 at them! People have different preferences for 'portrait' lenses; some like the 'natural' perspective of an 85mm (or even a 50), others prefer how longer lenses flatter perspective more. Some love the longer teles, such as 200 and 300mm lenses. And you'll get acolytes for both 100/105 and 135mm. I suppose it all depends on how you shoot; I like an 85mm, because it offers enough subject isolation, and has very little distortion compared to longer lenses, plus is nice and small and light and easy to move around with. But I also love my 105mm macro lens, because although it isn't as fast (f2.8 at 'normal' distances, smaller at closer distances), it is very, very sharp, and I love that. I favour accuity over 'character', personally. The shorter the lens, the closer you have to get to fill the frame, of course. So maybe a 200 or 300mm lens would work better for you. I also quite like getting right in people's faces, now and then, with a 24mm lens, which gives loads of distortion, but also can include a lot of context, which might be important in say an environmental portrait. Some love the 35mm for this. A long lens could allow you to work further from the subject, so maybe better for more 'candid' type portraits. But the possibilities really are all so subjective and about personal taste. You might find out that you end up only ever using an 85 or 135mm lens. Who knows? The 70-200m would at least let you explore a range of focal lengths.
So, that's a lot to think about, before we even get onto lighting...
Good luck!
