If we truly were the Land of the Free(TM) and had access to cars around the world, what cars would you expect to see in greater numbers in certain places of the USA? Canada as well, since they also follow our existing vehicle standards (except for their exemption being 15 years and ours 25).
Northeastern US (dense cities): Fiat Panda 4x4 & Skoda Yeti
Generalizing here, the Northeastern US gets a lot of snow, so they want AWD. Shitty roads, so they want ground clearance. They also want some storage space (as do many Americans), but may require something smaller and more maneuverable for parking in the relatively dense cities. European things are also considered stylish there. The upcoming Jeep Renegade is basically a Fiat Panda 4x4 anyways... May as well be popular there.
Los Angeles: Skoda & likely Latin American market sedans
Affordable sedans are king here, I think. With so many roads and a lot of sprawl, there are tons of them out there to get you across town. It's hard to come up with new sedans to add, because I think the existing best sellers would still be the best sellers (ie - Accord, Camry, Civic, Corolla). To add to the list of affordable sedans, I pick the Skoda Rapid, Octavia, and Superb sedans. They're stylish too. At least to me... I'd throw in some cheap rebadged Latin American market sedans as well simply due to their affordability.