Barrett made his debut off the bench against Samoa last month, while Laumape made his in the 24-21 second Test loss to the Lions last week.
Hansen rejected the idea that the selection of 20-year-old Barrett, who will start in the same team as brother Beauden, while their other broer Scott is on the bench, was a major gamble for such a high-pressure test.
Hansen says: “He comes from fairly good stock, I’m picking he’ll go all right.
“He’s a pretty cool, calm and collected kid. We wouldn’t have put him there otherwise.
“He’s very good in the air and the Lions will give him a lot of ball to catch. He’s a very skilful rugby player, I’ve got no doubt about that.”
Israel Dagg, who wore the number 15 jersey in Wellington, moves from fullback back to the right wing with Waisake Naholo dropping out of the squad to give him more time to recover from a head knock.
Prolific try-scorer Julian Savea was recalled on the other wing in place of Rieko Ioane, who scored two tries in the first test but fell ill after the second test and was unable to train this week.