With any manual lens, you can shoot Av and M on any canon body (or Tv with AutoISO).
Look for an adapter with an AF chip by Victor Lushnikov, they sell on ebay by user 'ml-gvalt' or from peleng8.com, they're the best. I've got them on all my MF lenses and adapters, it's what EdMika uses on his adapters too.
The aperture in EXIF will always be what you program the adapter to, like f/1.4 or so, it won't change. The camera will thus always think you're set at f/1.4 or whatever, no matter what you turn the aperture to. (From what I know, ZE-mount lenses work the same as canon lenses as far as the aperture goes).
Metering will always be 100% accurate in live-view. In Viewfinder-mode, sometimes it's off (not by more than a stop), I haven't done enough testing to see if it's lens- or aperture-dependent yet. histogram and re-shoot is easy to do.
For nikon G-lenses (ie, without aperture ring), you can get them on ebay too, just search for something like "nik* G (eos, ef) adap*" should get you some. Never tried them so not sure how well they work.