When was St. Michael canonized?

St. Michael was never canonized. He was first known as the archangel Michael and the Catholic church has never canonized angels. If the church wishes to pay liturgical honors to an angel, they give him the title of saint, since the angels have always resided in Heaven.

All three archangels, Michael, Gabriel and Raphael, have been given the honor of being called Saint. They are all venerated in a common feast on September 29th. St. Michael is known as a protector against evil forces and a soldier-angel. He is the most regarded archangel, and there are many shrines and prayers in his honor.