The preferred route for medical physics (in the US or Canada) currently is completion of a CAMPEP http://www.campep.org/campeplstgrad.html [Broken] and/or http://www.campep.org/campeplstres.html [Broken] program. Because the list of approved programs is kind of short, completion of a CAMPEP program isn't a requirement yet, but probably will be in 5-10 years or so.
After that you'll be eligible to take the ABR or the ABMP certification exams. In Canada you'd probably want to take the http://www.medphys.ca/article.asp?id=113 [Broken] certification exam.
Doing all that you'll be in a good position with just about all the clinical experience you need to get you started in a junior medical physics position in diagnostic radiology, nuclear medicine or radiation therapy.
I don't know much about the program at University of Houston, but I imagine the concentration in Dosimetry would give you a very good foundation to start a graduate program. It may be more geared to getting people started off as dosimetrists though, but that doesn't mean you also shouldn't do it if medical physics is your goal.