If you'd like to learn more about how the federal government unjustly railroaded Conrad Black, I can't recommend his autobiographical A Matter of Principle enough. A great eye-opener of a book.
Well that is his side of the story, which may or may not have any real truth to it. Personally I do not trust a single thing that Conrad Black says. As a Canadian I am upset at how he seems to have used his political clout to get himself a visa and likely have his citizenship restored.
It is well established that if you denounce your Canadian citizenship, Canada will give it back (and in fact, pretend it never happened), at least the first time. Conrad Black is not special in this regard.