I'm very sorry, friend. This first statement about Arianism being Christianity is simply false. Arius taught that Jesus was not co-eternal, but created at a finite point in chronos time. In Arius' own words, "There was a time when the Son was not." This contradicts the words of Christ, as recorded in the 8th chapter of the Gospel According to St. John, when he answered the Pharisees, "...before Adam was even born, I AM."
"The earliest Christians were not Trinitarians..."
Again, I'd point you to the Gospels, this time that of St. Matthew, 28:19, "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit."
So, I offer to you the words of Jesus Christ on these matters.
And, by the way, the first known listing of the New Testament canon, in the familiar modern form, was in a letter written by +Athanasius around Pascha in the year 367. This took place between the 1st and 2nd Ecumenical Councils.