Sounds like you are looking for an MA, not a PhD. You can do relatively extensive research on the topic of your choice through a thesis and it would better suited to your "professional" aspirations. I would suggest looking into the schools mentioned above. Also, if you want to go back to the great white north I would look into NPSIA in Ottawa (excellent ties to the diplomatic community) and the Munk School in Toronto. Both have high quality (and highly rated) professional MA programs. Goodluck.