Hi Susan,
If you can afford to, I would suggest keeping all your Zeiss lenses until you have had a chance to try them on the 20D for a couple of weeks.
You may find the convenience of autofocus and auto-diaphragm stop down with canon lenses outweighs the optical superiority but slower use of the zeiss. It probably depends on the kind of photography you mainly prefer.
Slow landscape work is fine with the zeiss, but anything moving - forget it.
I have the Canon 17-40mm f2.8L and it is a reasonable lens, but the corners are soft even at f11, and I find that difficult to accept for quality work. It does score points with the incredibly fast autofocus though, and in situations where slow work on a tripod is not possible, I shall use it instead of zeiss.
The Canon 70-200mm f2.8L IS USM is a superb lens, optically equal (maybe superior) to the zeiss 100-300mm, but far more usable. Again the autofocus speed is staggeringly quick and very accurate. The image stabiliser takes it into another realm, capturing shots that I wouldn't even consider without. 1/30th second at 200mm + 1.4x handheld is achievable!! I would highly recommend it and I shall probably not keep my 100-300mm because of this.
I am awaiting delivery of a 300mm f2.8L IS USM which should arrive on Thursday. Reports I have read rate this as possibly the best lens Canon make, and perhaps the best 300 2.8 ever - a grand claim, but one which seems to be backed up by images I have seen taken with this lens. I'll let you know how I get on with it.
Eventually it will come down to convenience. How much weight do you want to lug around, and how long have you got to set up the shot. There is little point in having a selection of fantastic glass, if it just sits at home because it's too heavy. I feel that the autofocus advantage may win out in the end for all but the wide angle lenses, where Zeiss have such superiority and focus speed is not such an issue.
I understand the Canon 24-70mm f2.8L is a pretty good performer and may well be a good replacement for the 28-85 (please post your findings if you do swap).
Everything in the end is a compromise and I would just reiterate try what you have before selling. You'll probably end up keeping the 35 and the 85(f1.4?) because they're special, and moving to Canon for the rest.
Cheers,
Matt.