There are a couple options---well, I see 3 from cheap to pricey. One is to get one of the dry bags with a fold-over seal, and attach it to the boat with a lanyard. Of course, you will be unable to photograph unless you take the rig out of the bag, then you're at the mercy of the salt spray, possibility of upset, etc. There is the option of a waterproof soft bag with window, like this one for $130 from various web sites:http://www.waterproofcases.net/slrcamera.html
I used something like that with my Nikon F4 film SLR, back in the day. But it was a bit clumsy. There are no submersible hard cases for that size camera with a tele lens.
I finally realized that taking several thousand bucks worth of SLR gear on a kayak is just not a good idea, and bought an Xacti by Sanyo----will take U/W shots, is HD, and takes stills. Nowhere near the quality of an SLR, but it's submersible, less than $300, and easy to use.
You can get an Ikelite hard case for the 7D, but be prepared to spend $1500 or so for true underwater capability.http://www.ikelite.com/web_two/can_7d.html
If you have a Canon G10, you can get form Amazon a nice U/W housing for $170 that is good to 130 feet down, and has fluorite glass window for distortion-free pix.
Lastly, Ikelite has several camera and case packages that might serve, mostly the point/shoot variety, but you didn't state what sorts of subjects you'll be stalking.