I tend to go with replacing all of one letter and planting 'Sunnydale' right over the real 'Sunnyvale', which I believe is just south of LA. On an amusing note, no matter how many times I change it, my Yahoo Messenger *always* gives me the weather for Sunnyvale, California.
Here's a note on the
Canadian school system (and a note that this is entirely BC-based, and it varies throughout Canada):
It's largely similar to the US system, but with a few key differences. Grade eight (though in BC, we recently switched grade arrangements in schools - K-7, 8-10, 11-12 to K-6, 7-8, 9-12, so that might have changed) is the first opportunity you have to pick your own courses. You are required to take one Math course (Principles, Applications, or Essentials), one English course (most schools only have one, save at the grade 12 level), one Science course (general science until grade 9), one Socials course (general until grade 9), and Physical Education. PE is only required until grade ten.
At grade nine, Science breaks up into Earth Sciences, Computer Sciences, Biology, Physics, and Chemistry. You are required to take one of them until grade 11. Socials breaks up into Civics, History, and Geography. Again, you are required to take one until grade 11.
Grade 12 is special. There is only one required course to graduate, that being English 12 (or Lit 12). For University entrance requirements, you need at least four
Provincially Examinable Courses - basically, core courses, these being: any Science, any Social Studies course except Civics, Law, Psychology, any Math course except Essentials, and any English course.
You also need 52 credits to graduate, collected throughout grades 11 and 12. Core academic courses are usually worth 4 credits, electives are usually worth 2. There are, of course, exceptions.
Now, once you've graduated, you have another decision: University, college, or work force?
University and college are two different places here: To put it simply, university is white collar, college is blue collar. College is generally the place one goes to either upgrade courses or to learn a trade - hands-and-knees work. Usually where the woodshop boys go. University is more academic; here's where you have your would-be doctors and lawyers.
Xander would go to College (which is also cheaper and takes less time), Willow would go to University. Buffy could, quite plausibly, attend either. Occasionally you get crossovers, such as the local Malaspina University College - carrying both trades courses and academic ones.
I can't think of anything else just now, but if you'd like more info, I can either remember or find it for you

Though I don't see a whole lot of W/T fics set in Canada...