Find out what he loved about photography
If possible, find out what camera and lenses he had when he worked, and what his favourites were. Someone who's worked for a long time as a photographer probably has some strong opinions about cameras, so you may find he strongly prefers a specific focal length, or zoom range. Perhaps even a camera system (did he shoot Canon?) or body size.
If he still has some old gear, either rummage through it and let us know what he owns, or better yet talk to him about it, and find out what he loved about it.
Primes or zoom?
Some photographers favour one (or a few) prime lenses. After a while, you get to learn the lens to the point you can frame the image in your mind. You can see the shot and how you want to frame it, and walk to where you'll be able to capture it from without putting the camera to your eye. Typical favourites are 35mm, 50mm, 85mm primes (perhaps longer if he's into sports photography, like 135mm or 200mm). If that's him, then you won't want to waste your money on a zoom lens he won't appreciate.
Some photographers like the versatility of a zoom lens. A professional is also likely to appreciate a fixed-maximum-aperture across the zoom range (i.e. lenses like the 17-55mm f/2.8 or 24-70mm f/2.8) rather than one which varies (e.g. the 18-55mm f/3.5–5.6). Typical favourites are something centred around 50mm (standard-zoom, e.g. 24-70mm) or something centred around 150mm (telephoto zoom, e.g. 70-200mm).
Note that the numbers above are in 35mm equivalent focal lengths (full-frame DSLRs, and standard 35mm film SLRs) while the 70D is an APS-C camera, which has a crop-factor of 1.6. The crop factor of the 70D basically means that the focal length (sort of) appears 1.6x longer than the number on the lens.
Note that this is compared to 35mm film, as I'm just assuming he used 35mm film—if he was into medium/large format, then things get a bit more complicated (and perhaps expensive!).
For example, if you find out he loved his old 35mm film SLR and his 50mm lens, then you can either get the 70D and a 28mm, 30mm or 35mm prime (equivalent to 45mm, 48mm, 56mm respectively). Or if it was a 35mm film SLR and a 28-70mm then you'd be looking for something like the EF-S 17-55mm.
What about full-frame?
Another good option would be the Canon 6D (though a little more expensive) as this will match more closely with the old 35mm system (again, if that's what he's used to), without having to consider crop factors.
Any old gear still lying around?
If he's got any old gear still, then some cameras are either directly compatible with older lenses (Nikon's mounts been the same for a very long time, Canon changed in 1987), and there are adaptors for some old lenses to fit new cameras. If he's got lenses that are high quality (seems likely if he was a pro) and still in good condition (check for fungus) then you may want to find a camera that suits those. Even if you buy a new lens with the camera, it could be quite fun to use the old lenses on a new body.
Finally, if he's likely to get into making videos with the camera (e.g. if he's into new technology, gadgetry, etc) then you'll probably want to get an STM lens. There's only a few around, but these are good for autofocus during videos on the 70D.