The Feast of the Trinity and Sola Scriptura

Tomorrow the Universal Church celebrates the Holy Trinity, God in three persons, yet one substance. In 325 AD, almost half the Catholic bishops in the world were starting to believe that Jesus was not truly God, known as the Arian heresy, following the teachings of the heretic bishop Arius. The conflict was threatening the political stability of the Roman empire at the time. Constantine demanded the Catholic Church convene a council and decide once and for all the nature of Christ. The result was the Nicean Council of 325 AD and the Church that Christ established put down the heresy and clearly ennunciated the doctrine of the Trinity.
   What does this have to do with Sola Scriptura?  Interestingly, there was no cohesive canon of scripture and the bible as we now know it was not yet on the scene until 393 AD. So one can't use sola scriptura to derive the doctrine of the Trinity, when it was not yet know which gospels and epistles would make up the New Testament.  It was only the magisterium guided by the Holy Spirit that was able to correctly ennunciate the doctrine of the Trinity and squash this heresy. This is not to say that the gospels were not available, I am sure they were and were read from the pulpits each Sunday, however, the scripture alone did not sort out this controversy. A Church with the authority given to Peter and his successors was necessary.