Canonization simply requires that a man be a saint. The Church does need to recognize the saint. This is quite simple - studying the man's life and his teachings. It is the will of God that people who are not saints give themselves away through falling into sin 'ye shall know them by their fruits'. It is usually quite easy to do this.
Secondly, the Church checks that the man taught strictly in keeping with the Fathers. If any of their main postulates are ever challenged the man is a fake. Also if the man is not part of the one true Church he is never considered, there is no way he could be a saint for grace is present only in the true Church - everyone who has partaken in the holy Communion in the Orthodox Church knows this (That is only a reference to how the partaker always feels changed afterwards.)
Miracles are not that important. Because false pretend 'saints' also perform 'miracles' and are often convincing and charismatic.
Saints can recognize other saints. Therefore, the main support comes from a testimony of one such or widespread support. For example, Elder Joseph was praised by many spiritual giants on Mt Athos and the community has accepted him as a saint. This is no easy feat on Mt Athos where saints are aplenty.
Miracles after death are very important, for they prove final success. Only in death are even saints secure in their salvation. On Mt Athos the bodies are examined after a period of years after death, thousands of years of experience have made a fine science out of studying the remnants of monks in order to find out if they attained salvation, if they don't they require additional prayer. Elder Joseph's body would have been examined long ago. Testimonies of people whose prayers to Elder Joseph were answered would have been taken into account.
I presume there is more to it. A saint will know another saint. Given that the Church clergy is spiritually wealthy, they will have no difficulty telling a saint's teaching from a fake just by reading, because grace would reveal the truth.
Obviously there is a deal more to it than I know, but I hope this was helpful.
When I was living in Los Angeles and attending USC, I would frequently visit the Orthodox Bookstore in Glendale, CA. The first time I visited was for the "grand opening" of Living Spring Bookstore, and this is how I met Anastasia, who is a pious Orthodox Woman. At the same time I met her parents. Anastasia was traveling often to Greece, to the Holy Mountain area to obtain icons, prayer ropes, etc for her bookstore. I was truly inspired by her dedication. That day was to be a great turning point in my life, for I had the chance to speak with her pious Father and Mother throughout the 2 two three hours I was there. They told me of their visits to the Arizona Monastery where Fr Ephraim is living and indicated the kind of pious life the monks were learning from Fr. Ephraim and the traditions of the Fathers carried with them to Arizona.
Just recently I purchased the Letters of Elder Joseph, Monastic Wisdom,' and I feel that he reveals very much in his letter to his disciples, in the same way that the collected letters of Fr. Ephraim in 'Counsels from the Holy Mountain.' In both books the term 'theoria' is mentioned often. In the Catholic Church the Ascetics and Mystics speak of experiencing God in various unions, but no more clearly than in St. John of the Cross , who says in the Ascent of Mount Carmel, "the likeness between faith is so close that no other difference exists than that between believing in God and seeing him. Just as God is infinite, faith proposes him to us as infinite. Just as there are three Persons in one God, it presents him to us in this way. And just as God is darkness to our intellect, so faith dazzles and blinds us. Only by means of faith, in divine light exceeding all understanding, does God manifest himself to the soul. The greater one's faith, the closer is one's union. with God. " [Ascent , Bk II, Ch. 9] English translation. ICS, Kavanaugh & Rodriguez/
My point here is that the uncreated light is made approachable thru the Word Incarnate and the Economy of Salvation revealed thru Scriptures. What is difficult to grasp more and more is that union with God is union with God and not God and something else. I mean faith is faith, yet the Saints knew it was faith they were exercising, they had purified their minds and hearts to discern the unlikeness to faith as apart from the purity that comes thru faith. I think that the Elder speaks about this in some place, I think is relation to the CHANGES that occur int eh soul adn how important to notice these changes. Could someone help me understand this term better?
In the western tradition I see it as discernment or in the Counsels of the Desert Fathers as Discretion, which Cassian covers in his conferences.
May Christ enlighten your minds and hearts to know his will and strengthen your will to keep it always,