Fr. Pedro de Corpa and Companions Franciscan Media:

Saint Pedro de Corpa and Companions’ Story
Another Saint of the Day for September 10
These five friars were martyred in Georgia for their insistence on
monogamy in Christian marriages...


Their names:

Pedro de Corpa
Blas de Rodriguez
Miguel de Anon
Francisco de Berascola

The article says they are saints. But couldn't find any details of the canonization online.

Are these friars really canonized?
If yes, who canonized them and when?
Is there any hagiography/biography written about them?
Fr. Pedro de Corpa and his Companions are currently not Saints, but Servants of God. There is currently a procedure for canonization started, which is now in the second phase.
An August 20, 2014 article in Our Sunday Visitor (J.J. Ziegler, Georgia martyrs died defending Church teaching, in OSV Newsweekly) gave the following information:

The path to the canonization of a martyr is different from that of other saints. First, a bishop begins the investigation of the life of the murdered person to find out whether his or her death is a true martyrdom — that is, whether he or she voluntarily accepted death inflicted out of hatred for the Christian faith. At this stage, the sainthood candidate is known as a Servant of God.
If the bishop approves, then the Congregation for the Causes of Saints continues the process in Rome. If the Congregation concurs that the death is a true martyrdom, then the pope may accept its decision and issue a decree on the martyrdom of the Servant of God. At that point, the martyr may be beatified and given the title “Blessed,” with public liturgical veneration limited to certain areas, such as a diocese, a nation or a religious community. No miracle is required for the beatification of a martyr.
If there are reports of a miracle granted through the intercession of the Blessed, then the Congregation may conduct an additional investigation. If the Congregation determines that the healing is a true miracle, then the pope may accept its decision and issue a decree on the miracle of the Blessed. At that point, the martyr may be canonized and given the title “Saint,” with public liturgical veneration extended to the entire Church.
The sainthood cause of the five slain friars — the Servants of God Pedro de Corpa and his companions (Blas de Rodríguez, Miguel de Añon, Antonio de Badajoz and Francisco de Beráscola) — is now in the second stage. In 2007, Bishop J. Kevin Boland, then bishop of Savannah, Georgia, concluded the cause’s diocesan phase, and the cause is currently under consideration in Rome.

Since the proceedings remain sealed until the investigation is concluded, I presume that there won't be official hagiographies yet until that point, besides stories written up by local investigators/historians/faithful.
At the present moment Father Giovangiuseppe Califano, OFM, the Postulator of the Cause, is overseeing the redaction of the final historical document which will be presented to the Congregation for the Causes of Saints next year.