I have the 1V and the EOS-30/Elan7 and I did have the EOS-3.
EOS-3: 95% viewfinder (I think). Sure, it's solid, quite fast, rugged, pretty heavy, good view-finder and eye-control which works alright after calibrating, since it has so many focus-points. AF is ok and pretty fast and accurate. It sort of looks like a beta 1V, but it doesn't have weather sealing to speak of. Instead of actual gaskets, it has "drainage-canals" in the plastic-composite shell around the camera, which will lead water away....but it doesn't really work in real-life (mine died from a short and very sudden rain-shower while I was out shooting and only had my t-shirt to cover it, which.....was disappointing). It cost me around $400 in 2005.
EOS-30/Elan7: Consumer-grade, small, plastic, light, eye-control focusing works ok after you have calibrated it, takes some time to get used to though...not sure about solidity although the build-quality itself is nice. (good controls, not very flimsy). AF isn't as good as the EOS-3 or 1V at all and it has less number of focus-points. Hunts more for focus in low light etc. Reminds me of a 450D/500D type of camera. I use mine when I want to go super-light with AF, it cost me $30 in 2013, remote shutter and printed manual included.
EOS 1V: King of the hill, 100% viewfinder, best and most accurate AF of the film-bodies, rugged, heavy (if you buy the battery-grip separately, so you can remove it, it becomes the size of your 5D III without a grip, I know, since I have that too). Same controls, look at feel as the 1ds MK II. (which I also have).
Solid weather-sealing (rubber gaskets all over, you can actually see some of them around the buttons on the most hated guy on the Internet's review here:
http://www.kenrockwell.com/canon/eos/1v.htm ),
Good customization options and it will survive wars and wildlife (proven, since it was used for that very purpose back in the day).
It cost me around $600 in 2005-2006 and I use the battery-pack that will also fit the EOS-3, which balance the camera with heavy lenses and gives you up to 10 fps. This will burn trough a roll in 3.6 seconds, if you are so inclined. ^^ (not sure about ass-kicking, but that will give your film-buying wallet a kick up the backside I suppose
)
I've used mine for everything from birds in flight, to air-shows, to portraits and landscapes and it hasn't let me down yet.
I also have the link-hardware and software thing (bought new, separately), but it's not compatible with anything newer than Windows XP I think. The software enables you to adjust custom-functions trough the computer, as well as gather EXIF-data from your rolls, you browse trough your roll-numbers and get a list of settings per shot etc....I tried it, but found that I never used it anyway, so it's not really missed.
All cameras are fully compatible with your EF-lenses, why you would go Nikon when you have invested in Canon-lenses is weird, besides, if you look at sports, wildlife and reportage from the late 90's, you see 80% Canon and 10% Nikon (and 10% others I suppose), so, at least in the professional-domain, the pro Canon-bodies were preferred over Nikon, most likely because of the focusing-system and sealed, quality L-lenses.
I would definitely recommend a "dentist used" 1V if you can get hold of one, with removable grip.
Make sure you know the camera history, as some of them may have seen pretty heavy use (journalism, sports, wildlife etc).
The 1V prints the film-number before the very first frame on every film, so you are able to tell how many rolls the camera has been trough, mine had 32 rolls trough it (or 1032 lol ) when I bought it. It resets to 0 after 999 rolls. You can also check id and number of films trough the custom-functions menu:
https://www.ephotozine.com/forums/topic/eos-1v-film-count-19600