Its just the same as a lot of 360 games being shown as a November 2nd release date at EB, but its pretty much just a placeholder date. We'll probably get the real date once Sony announces the date for the PS3 (if they go through with the plan to release Halo 3 alongside PS3).
I know the EB trade-in credit for it is $3, but that's all I know. I checked the computers for myself since I plan on getting a DS (and now you get it free with a DS), so I figured it could be $3 to put on my 360 preorder.