Is there a British or Canad. university grad school specializing in maritime history, especially privateering?

No, no such thing (I am studying history at present). The best answer for you is to get into the best university you can. If you'd like to read up more, the definitive works have been written by Kenneth R. Andrews, still alive I believe, who teaches or taught at the University of Hull in north-east England. His book, Elizabethan Privateering, is very inspiring. All the best, hope you get to be an expert in this field.