The “universally” accepted canon were canons as in multiple. There were multiple versions of the various scriptures and most were not universally accepted. Most of the writings and scriptures of the time were rejected by the council of Nicea and the version the council approved was heavily influenced by the need for Constantine to bring together the various sects and and beliefs into a creed that could serve to unite his growing empire. Again, anything touched by the hand of man, even the apostle’s letters, were shaped by situational politics and individual point of view of the writers. Even today, many denominations profess their interpretations of scripture, old and new. The scriptures should be taken as providing lessons and insights into God and not necessarily as the infallible word of God. Put your faith in the message of the scriptures and not on the literal infallibility of a set of documents shaped by mans interpretations of God’s message.
Somehow, I don't think Athansius was steered into what he thought were inspired books by Constantine.