From Catholic Answers:
Hi. I know that canonization is infallible, but I have read that the existence of some of these Saints, especially those of the early Christian church, are doubted historically. I've also read that there were instances where some saints were removed precisely because their very existence was doubted historically. Isn't this at odds with the infallibility of the canonization process?
Answer (from a staff apologist at Catholic Answer):
First of all, when the question arises concerning the infallibility of canonization, it usually centers on the action of a pope officially declaring someone to be a saint. There is debate among theologians as to whether or not papal infallibility extends to this, but according to the Catholic Encyclopedia most theologians believe that it does (for more information, please visit this link and scroll down to the heading, "Papal Infallibility and Canonization").