As far as tower visits go, phone ahead and ask to speak to the tower manager. Explain to him what you are studying and ask if you could come down and talk to him about the business of ATC. But, if you want to tour a tower in the U.S. you have to be a U.S. Citizen. So probably a Canadian tower would be best for you.
A few weeks ago I was talking to a guy at HOU
about aviation in general and we seemed to have a great conversation going. Later in the conversation I asked him what he did, he was the Regional Manager for the local FAA-ATC division! I asked him if I could tour the IAH
tower, and the next thing I knew, I was up there! Security did ask me several times for ID
's to make sure that I was truly a citizen of the U.S. Security at these locations is VERY tight! And I am sure that possessing a Commercial Pilot's license helped me out a little to boot.
Edit: add info
[Edited 2005-02-10 01:00:09]