I'm just wondering if I preorder from COG instead of steam will I still be able to play Dec 9th if I'm on the east coast of the U.S.? The store says available Dec 10. On Steam it says Dec 9th. I think that when I preorder on COG it will tell me Dec 9 but I just want to make sure before I preorder it. Thanks in advance!

It's a world wide simultaneous release on PC. The difference in time you are seeing is because of the time zone difference. The game is being released at midnight on the 9th->10th of December according to the UTC time zone EVERYWHERE, no PC platform is getting it sooner than another.

In short, yes, but check here for your local release time.