I'll add some content from my own experience.
If it was me buying with your budget I would be buying Canon, Unless you can afford a D300 or D700 Nikon. Simply because you get a more much for your money with a Canon 450D/XSi.
I'm not bias one way or the other I own both brands and just about every (fisheye) lens. Simply, either brand is great and more than capable. Forget the D40, D40X, D60 range totally if you want to shoot IDR Fused shots as they do not have AEB at all. The D70s, D80 are not as good as the Canon 450D/XSi. The Nikon D300 is the best small (DX) sensor camera on the market ATM with Canon sure to come back hard with it's next APS-C release.
The Nikkor 10.5mm Fisheye is a great lens for the Nikon but no better than the Tokina 10-17mm Zoom fisheye for the Canon (in fact the build quality feels better with the Tokina). These options cancel each other out. (Price could be the deciding factor).
The Sigma 8mm f/3.5 Fisheye is a great lens for either brand but is lesser to the Nikkor 10.5mm and the Tokina 10-17mm Zoom fisheye but more convienient because it requires less shots to complete the full 360x180.
Don't discount the Sigma 10mm fisheye when shopping.
About EV bracketing stops. The Nikon is only capable of 1EV steps (max 9 with the D300) where the Canon can go 2EV steps (max 3)
For blown out windows with the Canon I would shoot +1EV, -1EV, -3EV or 0EV, -2EV, -4EV and this will typically give you enough to balance the lighting. Remember you can pull many EV stops from each of every RAW image. Certainly 2 full stops.