If you drop the Cornell's scholarship then you'll be forgoing a sure financial benefit for something that's uncertain (getting into M7). I would consider the worst case scenario of you dropping the current Cornell offer, apply next year and don't get into M7: are you comfortable with that?
Getting interview to M7 this year is no guarantee of scoring a spot next year, if you were to be in a waitlisted then that's marginal, and applying R1 next year may help.
I was in a similar situation last year, forgoing a full ride scholarship from a lower ranked school and ended up not getting into my target school. Luckily I scored a spot in M7 in R1 this year, but I did have a lot of restless nights worrying about my applications.
I reckon what you should do now is to talk to an admission consultant, let them have a quick read of your profile, see what they say. If there's a clear red-flag that can be fixed quickly and results in M7 admission, then there's a good ground for dropping Cornell's offer.
P/S: also consider that if you do get into M7, most likely you'll pay full fee (since you're a reapplicant).