can i add the sims 3 to the ea app if i bought the game on steam

Magictastee​  Does your Sims 3 Store account use the same email as your EA App account, which is different than the one tied to your Steam account; or does the Store account use a different email than the EA App account?  And are your EA and Steam accounts linked?  Don't link them (yet) if they're not already; just let me know.

I have this same question. I tried Puzzleaddict’s suggestion but it will not accept my game CD key (says it’s already been used). Is there a way to merge my Sims3 Store account with my EA / Steam account? They are under different email addresses. 

@daylighter99  Yes, you can register the CD Keys that Steam provides you.  They're under Manage, or Properties; they've moved around a bit.  All of them are 20-character codes, so you'll know them when you see them.  You can add them within the EA App, or better yet, on the old Sims 3 site (use Register a Game at the bottom of the page):

https://store.thesims3.com/

If you do use the old site, be sure to login with the same email address and password you use in the EA App.

This doesn't prevent you from playing through Steam, and in fact you can buy Store content through that website, and points through the EA App, and use the content you've purchased in your Steam install.  That's my setup: everything is registered with EA, but I only use the Steam version, along with my Store worlds and other content.