They prayed either to God the Father or to Jesus Christ. The reference to Jesus as Lord in Acts 1:21 might suggest that he is in view. However, they were also taught by Jesus to address their prayers to the Father (Luke 11:1–4). Thus, it is more likely that he is in view1 especially given the reference to the casting of lots (Proverbs 16:33).
24 And they prayed and said, “You, Lord, who know the hearts of all, show which one of these two you have chosen