I am curious to know what people that photograph other things would do too! Thats why I said that.
But if you want to know, I like to photograph people working, not rich people, people from deep Brazil, where I live now. In the farms for example.
(I'm talking about $2000 in US prices, of course).
Firstly, I echo distant.star's comment - to be thankful (that many people would love to have a 5DmkII and $2000 available to them - and I'm sure you know that from Brazil too).
I do quite a lot of 'people in an environment' style photography - eg recovery / therapy camps for adults and children, church events, some casual sports, etc - though I wouldn't say this is my 'preferred' photographic genre, nor even an area I have most of my skill in.
The lens that I find is the most useful on my Canon 7D for most of my 'people shots' is the very good Canon EF-S 15-85mm. That lens covers equivalent of 24-136mm in FF format. I have also used and owned a good copy of the Canon EF 28-135mm, and the EF-S Canon 18-55mm.
So while it depends on the type of environment you would photograph people (as you said, on farms) - eg mainly outdoor, in large expanses, or up close, detailed work, etc - for FF I would want something of the focal range of the Canon EF 24-105mm L - which gives you both the possibility of context (eg wide angle) and some telephoto (at 105mm). With FF one has more potential for thinner depth of field, even with an f/4 - that can produce some shallow depth of field and have decent bokeh.
Next I would get the 70-200mm f/4 L IS - which would give you some creative potential for more telephoto. And having IS is invaluable here (especially @ f/4). I think if you shopped around and were careful, you could buy both the 24-105mm L and 70-200 f/4 L IS new for about $2000 US. If new wasn't a possibility - I'd get one (or both) of them refurbed from Canon.
While I own and prefer the Canon 70-300mm L over the 70-200mm f/4 IS - this 70-300mm L is more expensive -and perhaps there are fewer 'deals' going on it too. The 70-300mm L really shines on my 7D, and I've used that for people photography too, it has great sharpness and exceptionally good bokeh for a relatively slow telezoom.
So, in summary if you can - perhaps get the 24-105mm L IS and the 70-200mm L f/4 IS. Good to great image quality from both lenses, relatively light (eg transportable, etc) - and both have USM and IS - which are really helpful features to have. And after using these 2 lenses for some time, you may have saved some money and will find out if you need an other lens, eg a fast prime, and at what focal length, or maybe an ultra-wide angle (for that 'special UWA effect'). I doubt that I'd want to get a prime unless you have some time and experience in shooting the style of photography that you're talking about.
Hope my input helps.