Hey JJP05,
I actually have the exact same decision to make =P (I'm Canadian too so random! Buttt I am an undergrad in an American uni). I'm planning to go to both admit days (I'm not sure when Columbia's is, but I'm going during my school's spring break which is the last week of March) because that is when Yale's admit day is.
I honestly feel 90% about Columbia because of my particular research/career goals. I'm a neuroscience major, and have a strong neuroscience research background and my goals for getting an MPH are to be able to do population based preventive studies with mental health. So for me, going to a school that has a lot of emphasis on mental health in the epidemiology department is really important. I also want more of a hands-on MPH experience, as much as I love doing research - I don't really want research intensive curriculum. I feel that Columbia's new curriculum is very unique in the amount of field/practical experience it will give us, whereas Yale is more research based.
You might also want to consider what schools have professors/faculty/affiliated centers doing the kind of research/projects you are particularly interested. Contact these people and see what opportunities they may have for you? I'm already in touch with a couple of professors at Mailman, and I'm really interested in their research/career paths so I think Columbia really is the best place for me.
I hope these things helped! Both are great schools for Epi though. OH, another thing to consider - Columbia admits 1200 students, Yale about like 120.. So class sizes will be a BIG difference.
Are you doing the Global Health concentration at Yale with the CDE? I got into the Global Health concentration in both schools - but that factor may weigh into your decision for what school you may want to attend as well (if you're really interested in studying abroad)?!
AND FINALLY! MONEY! I honestly haven't gotten very helpful answers from Yale about financial aid for INternational students, and I'm REALLY not looking to pay full tuition/take out thousands and thousands of dollars in student loans. So I'm trying to see what Columbia has to offer for me with regards to financial aid... its' tough for us =(, but I thinkkkkk Columbia is pretty good with giving aid to Canadians, so let's cross our fingers......
GOOD LUCK, and let me know if you have any insight for me too!!