<p>1- It's hard to say, but my guess would be Quebec just because McGill fits within the provincial education system (though admission is not as tough for Quebeckers). For the sciences in general, the cegep curriculum is pretty solid (it's sort of equivalent to a freshman year, all cegep graduates start in U1, not just in science) and I've heard from at least one American that it prepares much better than most US schools. Also consider the fact that, back in my days at least, practically all honours physics students were Quebeckers. Of course that doesn't mean much at the individual level.</p>
<p>2-It is very ethnically diverse, unless your only criterion is skin colour. Also very religiously diverse, but religion is mostly a private thing so it doesn't show so much. But I can tell you I had never met a Zoroastrian before coming to McGill. Socioeconomically, obviously the international and out of province contingents are relatively well-off, but there's a wide array of in-province students and the socio-economic ladder in Quebec isn't very large, so differences aren't very apparent.</p>
<p>3-12 is the minimum number of credits in a regular semester to be considered full time (a standard undergrad course is worth 3 credit). 15 is the number you'll need per semester to finish without taking summer classes. It's not a bad idea to take one easy course in your first semester. It'll ease the workload (depending on what your used to, it can be quite a shock) and can compensate GPA-wise for bad results (or bad luck if you wish) in at least one class.</p>
<p>4-They're not invisible. You can look up the sports section of the McGill Tribune to see which are more popular (I'm guessing hockey and football, in that order), but there's much more. I just don't personally know about it.</p>
<p>5-It depends on the TA. Some are really good, some are terrible. You can inquire with your departmental student society to know if a particular one is good, provided that the TA has TAed before. But you may not have much of a choice of tutorial section anyway.</p>
<p>6-It shouldn't be hard, provided you have the prerequisites. Yes, you are allowed to take courses outside your own faculty, but, again, it's a matter of prerequisites and maximum class size (usually not a problem, but preference will be given to in-faculty students if there is a limit and the class is full).</p>