The Sims 3 is in our script repository, so you should be able to install it by launching PlayOnLinux, clicking Install (the + icon), selecting it in the Games directory and following the instructions from there. Unless there is some problem with your computer's configuration, that should work fine :)
There have been some issues in the past, however, and sometimes we can't find a solution, so what I'd do is check with your retailer if you can get a refund in case the game doesn't work, since you never know.
Disclaimer: I'm a noob, not a dev; my advice is only a guess.
Attention : Je suis aussi noob que vous, prenez mes suggestions avec un grain de sel ;)