I will be gold later this year on CO (based on travel scheduled so far, but at a minimum silver). I will be spending alot of time in Seattle and traveling once or twice to San Francisco. I know CO doesn't fly there (at least there aren't any flights listed on line). I also know that CO elites are eligable for Upgrades on Northwest. My question is if the Northwest "flight" is a codeshare with Alaska does that still apply? Since it is Alaska metal my guess is that it doesn't apply, but I wanted to ask here to be sure. I am not worried about the 50% EQMs from booking on NW becasue it is an H fare (100% EQM on CO).

The only other reason I am thinking of booking on NW is that I have Amex Business Platinum and with it I can use the NW lounge. Will that work given this is a code share as well?

Thanks everyone for any help!