It's the first series in a while where I have a really hard time predicting some tendencies or potential scenarios since it's such an unknown to me. Miami or Boston in 6 wouldn't surprise me, for example.
On one hand, I think that the adversity (and the great defense) faced by the C's against Toronto will be of a huge help against Miami which has basically faced little to none adversity so far (except for game 4 against the Bucks), in the sense that our players will probably feel like they are facing an "easy" defense compared to Toronto's. The Celtics know what to do and what to expect of each other in tough do or die situations while the Heat has been unproved so far on that side (and although Butler is playing great I still don't think he has what it takes to perform on that stage). On the other, what scares me the most about Miami is their spacing and ball movement, as well as a number of players who I could easily see go off against us (like Dragic and Crowder).
I guess the biggest key to the series might be how Bam Adebayo performs and how he impacts us with his rebounding and defense. But I'll gamble on the adversity and Hayward's comeback at some point to say Celtics in 6!