What we today know as the Catholic Church came into its own during the so-called Dark to Medieval Age in Europe. Before then Christendom was a disparate group of mainly unitarian, binitarian and nascent trinitarians. For example, during the time of the councils, like Nicea in 325AD., you had unitarians arguing against nascent trinitarians.
So the myth that the Catholic Church, let alone Emperor Constantine, created the biblical canon as we know it today is just that, a myth!