I disagree with Konic concerning the passport question. In any of those countries, if a university offers you a post-doc level academic job, it won't be hard to receive a work permit, no matter what nationality you have. Highly qualified immigrants are welcome most anywhere.
I believe the first hurdle would be the value of your PhD. For example, I've heard that PhD's from not very high ranking UK universities won't necessarily be accepted as equal to US PhDs in the US. Jobs requiring a PhD in the US might not be open to you if you received your PhD somewhere else. It all depends on the relative "image" of your university/department and on achievements which underline the value of your PhD such as high-impact publications.