This issue first popped up with the Canadian Echo Hatchback (1st gen Yaris). Look at this thread for a start:
2004 Toyota Echo Hatchback (Canadian model) - CarSpace Automotive Forums
Good news is that the 2nd gen Yaris is a ULEV vehicle (Ultra Low Emission) whereas the Echo HB was only LEV. The new Yaris should be California legal - therefore "US anywhere" legal!
Good luck,
Paul