I don’t expect any surprise here. Trump doesn’t want to feed the “Trump is unpredictable and shouldn’t have his finger on the button” nonsense.
Pence is not my favorite but I could see why Trump would pick him:
1)midwestern roots (MI, OH, etc.)
2)vanilla personality
3)GOPe connections
4)mainline conservative reputation
I don’t see how a surprise pick hurts Trump so long as it is a decent pick. It will actually demonstrate how Trump can run a tight ship with no leaks.