What Pope canonized St. Tarcisius and when was he canonized?

Tarcisius was not canonized. He was proclaimed a saint by early
Christians because of his martyrdom. The canonization process did not
come into existence until the 12th century. In the primitive Church,
martyrs were immediately recognized as witnessing to the perfection of
Christian life on earth, having shown the ultimate proof of their love for
Christ by the offering of their lives. By the sacrifice of their lives
for Christ, they attained Heaven in eternal glory and were indissolubly
united to the Lord, the Head of the Mystical Body.

Today only the pope can declare a saint. In the time of Tarcisius any bishop could declare a saint.
Tarcisius was not canonized. He was proclaimed a saint by early
Christians because of his martyrdom. The canonization process did not
come into existence until the 12th century. In the primitive Church,
martyrs were immediately recognized as witnessing to the perfection of
Christian life on earth, having shown the ultimate proof of their love for
Christ by the offering of their lives. By the sacrifice of their lives
for Christ, they attained Heaven in eternal glory and were indissolubly
united to the Lord, the Head of the Mystical Body.

Today only the pope can declare a saint. In the time of Tarcisius any bishop could declare a saint.