Actually, sorry to dissapoint you but Harvard is known among the dental world for having not so hot a clinical program (academics are top notch though). So, if you're going to practice dentistry after graduating, and looking for an associateship, I can guarantee you that having gone to harvard will be a NEGATIVE! Yes, you can probably impress patients, but when you pulp expose every other cavity prep, they'll start to understand what the dentists already know (which is, a harvard grad needs a lot of extra practice to do good dentistry!)
Now, if you want to go into ACADEMIA of dentistry, do RESEARCH or straight up specialize, then of course harvard is the way to go. Unless you fail (which is VERY hard to do at harvard dental since it's esentially a pass/let's talk about it and then you pass system), you are pretty much good to go for speciality if you get the board scores (i.e whereas for other schoools, your class rank will matter, from harvard it will not).
If you're 100% sure you'll stay in canada, go to McGill. Otherwise, you have to go to Harvard. Having a US degree, you can practice anywhere in the world after taking a clinical exam (way easier than any regional boards in US), and Harvard's name WILL impress patients and dentists INTERNATIONALLY (again, NOT in the US b/c dentists here know clinical at H is lacking). The cost of education at Harvard is NOT very high compared to other US schools, and believe me, in 4-5 years interst rates will drop, you can consolidate your loans at like 3-4% and take as long as you freakin want to pay off your debt b/c it will be like free money.
The point is, Harvard is a VERY GOOD school, but NOT if you plan to be a general dentist (i.e practice upon graduating).
Make the best decision for you!