I know this'll be necro'ing the thread, but just to let you know if interested, CAW can be used with Steam, but it does require a registry tweak to do so. Also, remember Steam's version of Sims3 is 1.67 unlike Origin's which is 1.69.
You can find instructions here in Steam's "The Sims 3: Community Guides" https://steamcommunity.com/sharedfiles/filedetails/?id=277022926
And yes, it works. Haven't actually figured CAW out yet, but I have followed this guide and can use it now.