While we can privately invoke the intercession of anyone we hope is in heaven or purgatory, a person cannot be invoked in public prayer—prayer done under Church auspices—until the Holy See has declared the person blessed. This ruling excludes also the “venerable” from public reverence. Canon law states, “Only those servants of God may be venerated by public cult who have been numbered by ecclesiastical authority among the Saints or the Blessed” (CIC 1187).
To find out the status of Cardinal Gibbons, we called the Archdiocese of Baltimore, and they said that they know of no steps taken toward his canonization. He has not been declared a servant of God, venerable, blessed, or a saint.