No difference between supreme authority and infallibility? Come now, that is pretty bizarre to say the least. Infallibility is what protects the pope from erring on doctrine and only when he meets the criteria in the Vatican Council.
Supreme authority is the fact that no authority is higher than the pope. If even acts of the pope in his fallible capacity demand assent, then you have to say that these are infallible, since they came from his supreme authority given by God. But we all know that the pope can err under certain circuмstances. How do you reconcile this, unless you say that he does not exercise supreme authority when speaking in his fallible capacity?
And then, how do you escape the problem of your position, which is that it allows us to judge the Holy See any time it does not speak ex cathedra?
Heresy is a proposition in contradiction to Divine revelation. Therefore, a pope condemning heresy is speaking on a doctrine concerning faith or morals which has been handed down in the Deposit of Faith and is binding on all Christians, and therefore infallible.
You're distorting the matter. I say we ARE bound to believe in canonizations just as we believe in any act of the pope in his fallible capacity. But just like an encyclical, for example, in which he does not specifically bind all the faithful, we are not bound to believe that he is necessarily free from all error.