You might check Thule's European fitments for the Vauxhall Astra, assuming GM markets the wagon version in Europe. For example:
http://www.fasteronline.co.uk/Thule-...em-p-2335.html
The 2008 3 & 5 door Opel Astra models will be marketed in the US late this year under the Saturn brand using the Astra name; however, I didn't see where the Wagon version was being offered. Instead, it appears as though GM is marketing the Opel Antara -- a compact crossover SUV -- as the Saturn Vue with a hybrid powertain option to fill the wagon-market niche.
Interestly enough, GM's Saturn Sky Redline model is being marketed in Europe as the Open GT: globalization is an interesting thing.