And that's going to be a good thing for US buyers.
There was a time, however brief, when GM's Saturn division was set to be a sister brand to Opel. Of course, this was not long before Saturn was killed off during GM's bankruptcy. But GM liked the idea of a "Euro" focused brand in the US, so Buick was called in as the replacement. The Opel Insignia became the Buick Regal, and the plan has so far worked very well. In fact, the next-generation Regal, set to arrive in 2017, looks like it's going to be imported directly from Germany to US shores.
At the moment, the Regal is built in Ontario, Canada. GM has yet to make it official, but it's been confirmed that Germany's Russelsheim plant "has been chosen for the assembly of a future model which will be sold in the US under the Buick brand name in the second half of the decade." Having the next Insignia and Regal share the same production will be a good thing for US buyers. GM is thinking the same and there's ongoing talk on how to further intertwine the Opel and Buick brands in terms of platforms, styling and features.