STL-ATL : Yes, and as a Plat you should clear instantly on the medallion upgrade anyway even without the SWU, assuming upgrade space is available.

ATL-CDG : Yes, W (premium voyager) is upgradable to business class. However, there needs to be "O" inventory available on the AF flight. There is no automated waitlist, so you'd have to keep checking for O inventory to become available and call quickly to snag it.

CDG-PRG : No, not unless somebody messes up and accidentally tickets the upgrade.

Note: The ticket must be reissued before departure with the SWU show as 'closed', especially for the AF segment since that reissue takes longer.