In general, you aren't going to specialize to anything beyond 'physics' at the undergraduate level. You can choose option courses at the senior level that will be more towards the area you are interested in, but you'll end up with the same B.Sc. in Physics as people who want to do general relativity and cosmology, string theory, quantum optics and quantum information, etc.
Looking at the McMaster website (specifically http://physwww.physics.mcmaster.ca/cgi-bin/display.pl?page=programmes ) I'd say that you'd want to do the Honours Physics program, either the Core or the Theory & Computation stream. The Combined Honours Math & Physics would also be good, but looks to be heavier on the math so wouldn't get you into the physics as quickly or as deeply, until grad school. This can be a good thing, but only if you really enjoy the math at least as much as the physics. The first time you'll get a taste of introductory quantum should be as part of PHYSICS 2C03 - Modern Physics in second year, with a full course of it in 3rd year.
Once you get to grad school, UBC and U of T have large physics departments that should have whatever you're interested in, and U of Calgary has a new Institute for Quantum Information Sciences (
http://www.iqis.org) putting it up along with Waterloo as one of the top places in Canada for that area of research specifically. Any of these places, and pretty much anywhere else, should also be good for undergrad.
As for what to take in high school, anything math (especially calculus, and linear algebra if they offer it) and definitely whatever physics courses are available. Chemistry is useful too, although it's not strictly necessary and you probably won't ever study it again after first year of university. (Note that when I say not necessary I mean for learning physics - some universities may have it as an entrance requirement to the physics program, so you should check that out with everywhere you're planning on applying).
Also, check out university websites. Look for the Physics & Astronomy (or similar) Department in the Faculty of Science and read over course descriptions, degree requirements, etc. Also look for the online versions of the university calendars for that info. Guess that's a fair bit of information, hopefully it answers your questions - feel free to ask more though!
Mike
