The word "saint" means "holy one". It comes from the Latin "sanctus" (holy, as an adjective, or "holy one" as a noun). The archangels are certainly holy ones, because they are in the presence of God at his heavenly throne, as Scripture teaches.
Do you pray to angels as you do to saints?
St. Michael the Archangel, defend us in battle, be our defense against the wickedness and snares of the devil. May God rebuke him, we humbly pray, and do thou, O prince of the heavenly host, by the power of God, cast in hell Satan, and all the evil spirits, who prowl about the world seeking the ruin of souls. Amen.
Try it sometime when you're under spiritual attack. The devil hates it.
how does the intercession of an Archangel differ from that of Christ ?
Sorry, I believe God will let nothing happen to me that he has not ordained. And everything that He has ordained, though I may not understand, works for my good and benefit. Like Job, the devil cannot attack believers unless God foreordains it. God is our shepperd and He will take care of His sheep.