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The squad will face the Barbarians in Cardiff on November 30.
McNicoll and Halaholo, who qualified through the residency rule, are among five uncapped players in the squad alongside Taine Basham, Shane Lewis-Hughes and Ashton Hewitt.
The 35-man group for the non-cap match includes 22 members of the Rugby World Cup squad that finished fourth in Japan earlier this month.
However, captain Alun Wyn Jones was ruled out injured, while England-based players Dan Biggar and Rhys Carre were unavailable for selection as the game falls outside the designated test window.
"It is great to get the squad announced and get the ball rolling on our first meet-up and first fixture next week," Pivac said.
"This Barbarians game is a great chance for us as a new squad and management to get together and to set the scene for what we are looking to do. Having this opportunity ahead of tournament rugby in the Six Nations is ideal for us."
Former Scarlets boss Pivac will face a Barbarians side coached by his Wales predecessor Warren Gatland, whose 12-year stint with the national team ended after the World Cup.
Forwards: Elliot Dee, Ryan Elias, Ken Owens, Rob Evans, Wyn Jones, Nicky Smith, Leon Brown, Samson Lee, Dillon Lewis, Jake Ball, Adam Beard, Bradley Davies, Seb Davies, Taine Basham, Ollie Griffiths, Shane Lewis-Hughes, Ross Moriarty, Aaron Shingler, Justin Tipuric, Aaron Wainwright.
Backs: Aled Davies, Gareth Davies, Tomos Williams, Sam Davies, Jarrod Evans, Willis Halaholo, Hadleigh Parkes, Owen Watkin, Owen Lane, Josh Adams, Steff Evans, Ashton Hewitt, Johnny McNicholl, Hallam Amos, Leigh Halfpenny.