Doing a quick check of the "big 3" U.S. airlines, it seems that it is fairly tough to get an upgrade on an international partner airline, even an alliance partner.

Delta: Used to have upgrade awards on the Qualiflyer partners (SR,SN,Austrian); now, only offers upgrades on Korean and Singapore(?!). No upgrade awards on major partner AF. Upgrades on codeshares are allowed.

American: Upgrades on Cathay Pacific. Upgrades on codeshares not allowed.

United: Upgrades on LH. Upgrades on codeshares -- not sure, I think not.

Continental: No partner upgrades that I can find. Codeshare upgrades allowed, at least on Virgin Atlantic.

Northwest: Upgrades on KLM. Codeshare upgrades -- yes, I think.

I mined most of this from web sites, some may be incorrect. So corrections are welcome!