Like to be honest, they couldn’t have picked a better seiyuu to play Sakamoto than Hikaru Midorikawa. And here’s why:
His nickname in the voice acting community is “Mr. Perfect”; he has this nickname because he’s got a voice that’s really suited to play stereotypical bishounen prince characters, AND because he hardly ever has to do more than one take when recording his lines; he usually gets it just right after the first take. There have actually been a couple jokes in anime/video games about how great of an actor he is (see the Fate/Zero OVA about Diarmuid, and the joke commercial where he voiced EVERY character in Tales of Destiny 2).
Hikaru Midorikawa is literally the Sakamoto of seiyuu okay.