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The problem with the EU situation is it's unlikely to be resolved to a tight knit federation. If you don't believe in a Federal Europe, don't belong to the common currency and your population dislikes the freedom of movement (which is a debatable point, since we have more citizens in Europe than European immigrants) then why stay committed to a looser union that may be forced to try and resolve to a tighter federal union.
So Boris is right, the US wouldn't sign up to a halfway house as they already have the complete package. They also wouldn't join a federation with S. America and Canada.
There is a distinct possibility that the next phase of the EU and Euro will be a need to create Federal Europe brought on by the effects of a single currency.
It would never create a federation of states with a common currency, free trade and freedom of movement, and a mix of centralised and sovereign powers?
No, probably not.