It'll run but it won't run great.
If you dumb down the settings for your MacBook, it'll be ok.
It won't be snappy, and it'll feel a little bit slow.
Your iMac on the other hand will handle the game pretty well.
On the same hardware, the Sims 3 runs a lot better on Windows. (Bootcamp)
I haven't tried the update yet, which apparently fixes Mac OS X graphics problems though.