Is it true that Gabriel (peace be upon him) raised the Samaritan, and that Pharaoh raised Moses (peace be upon him)? If so, how did Gabriel (peace be upon him) raise the Samaritan, and why did he not raise Moses (peace be upon him) instead?

As for Musa, the Prophet of Allah, he was raised in Pharaoh's house, and his story is mentioned in the Qur'an and Sunnah. As for Musa the Samaritan, there is no authentic report that Gabriel raised him. Rather, it is mentioned in books of stories and history that Gabriel raised him among the mountains. It has been said regarding this: "If there is no help from Allah for a youth, then disappointed is he who hopes, and disappointed is he who expects. So Musa, whom Gabriel raised, is a disbeliever, and Musa, whom Pharaoh raised, is a messenger." Whether Gabriel's raising of the Samaritan is true or not, there is no strangeness in that, because the guidance of divine grace is solely in the hand of Allah.