I've had Canon and Ike housings, and there is really no comparison: The quality of the Ike housing is MUCH better. I would have no fear taking the Ike housing deep, and while some I know have taken the Canon's deeper than they are rated for, the plastic does not inspire the confidence in me to do so.
The stainless latches are one thing I first loved about the Ike case. They're great! WAY better than the plastic snaps on the Canon.
The back plate on the ike is one piece, and you can clearly and easily see the o-ring all the way around. The Canon's o-ring view is blocked in many places.
The Ike is better suited for adding on external lenses, has more options as well as more attachment options. Not all of the Canons can even handle an external lens, and those that do require an adapter.
The Ike is a 2-piece design welded together by those latches. It comes apart in two separate pieces to easily clean every nook. The Canon is held by the plastic latch on one side and a hinge on the other. Strong enough, I know, based on my own use and many other happy users, but be forewarned that if you do shore diving sand will get into the hinge and there is no way to clean it out, leaving you with a case that makes a horrible, scary crunchy-scrapey sound everytime you open/close it.
The Canon wins on a couple of levels, however. The flash diffuser works better, as I think the Ike case is really designed to be used with a strobe. It also has a nice little thread/retainer, unlike the Ike which is held on by spring compression, making nearly everyone I've talked to have at least one close call or outright lost diffuser. (I jury rigged a little keeper system for mine after the one close call)
The Canon case also fits nicer in your hand for one-handed shooting, while again, the Ike seems more designed to work with a handle/tray and strobe.
In a similar vein, the Canon comes with a good wrist strap, or you can easily attached a better system such as a coil lanyard or retractor. The Ike housings come with a horrid rubber strap that I don't trust for a second. Without spending extra money on a tray and handle, there is no good way to attach a different lanyard or other retention system.
Once you add the handle/tray to the Ike, it is even more of a huge brick than before. Not a big deal in many cases, but if you're looking for a fun little camera to take on vacation, or perhaps hiking along a waterfall, you're now faced with a big chunk of hardware, making the Canon case more versatile for non-scuba use.
And the Canon, of course, is a LOT cheaper.
There are tradeoffs for everything. Ideally I'd have both, so I could switch back and forth depending on mood and planned use.
