It's not really possible, as the recent mess should illustrate. Europe is simply too heterogenous for that to be feasible in the foreseeable future.
That's very unfortunate but understandable. A federated Europe may not be practical, but one would hope, at least from an American perspective, that the EU would remain a legitimate organization. The EU is a precedent, in that, it is the first continental union in European history to not involve conquerors or bloodshed.