$200,000 extra to go to Cornell is IMHO insane. Taking on this much debt looks to me like a big mistake, even for someone going into a relatively lucrative practical field such as computer science. Cornell is a very good university, but Waterloo is also a very good university. Of course this is $200,000 in US money, which right now translates to about $266,000 in Canadian dollars. This is a LOT of money.
I don’t think that you have passed the application deadline for Dalhousie either. There are also some very good smaller universities such as Trent and Acadia (and probably Mount Allison) that you can still apply to. You have probably missed the deadline for scholarships, but not for admission in September.
I think that your realistic choices are Waterloo, or Waterloo for a year and transfer, or find another university in Canada that hasn’t passed the application deadline, or take a gap year and reapply.