First you have to decide Nikon or Canon. Next forget about the idea of not upgrading if you want the best available. Cameras are evolving so rapidly that your newest and best may be out-dated by the time you use it. Rather then worry about having the absolute best find one that is good for your needs and abilities and go out and shoot,shoot,shoot. For example the Nikon D3 is there newest pro camera(seeAlex's review for info) but there are rumors that the D3X will be out soon. Should you wait or take the plunge now? Tough questions and it gets more difficult when you consider all the D2Xs that are now available for a much more reasonable price.
As for housings the best may be easier to pick. Look at Subal and Seacam. I know you have dealt with Ryan before. He is a Subal dealer. Steve Frink is the Seacam dealer. Next time you are in Florida stop at both their shops and handle the housings. Whichever one feels best and fits your hands is the way to go.
I hope you're not thinking of switching before Wakatobi. There is too much new IMO to do that. Go with your present setup which you are already getting good shots from.