@gearstache had the answer, I think (full credit to him!):
Brest, France and Brest, Belarus; with Nuremburg, Germany in between...@jafe that's some cheeky wordplay...
but it's disappeared and I don't know where it went!
Here are the explanations:
Europa's endowed with a beautiful pair,
Between them some stunning Bavarian flair.
The Bavarian flair between them refers to Nuremburg
If you love nice châteaux, hands up in the air,
Surrender completely to Brittany fair.
Brest is in Brittany, and Brittany is in France and has chateaux...also please no France surrendering jokes!
A volatile border's now marked by a bug,
The Bug River separates Belarus from Poland...ie. Poland from the former Soviet Union.
A former pole's become a prominent hub.
The city of Brest was formerly Polish, but is now in Belarus.
A trial site's FC's boys take pride in their club,
Hey, pour me a pint in that old Frankish pub!
Refers to 1. FC Nuremberg and the Nuremberg Trials!