"For Hadleigh, my goal for him is to make him a No 3 for the side, and he's committed to trying that," Marr said.
O'Leary will likely join skipper Greg Smith and veteran Mark Fraser in a few overs of spin, as Whanganui will be without pace bowlers Oscar Mabin (school commitments), Fraser Kinnerley and Nick Harding (family duties).
Wellington-based local batsman Matt Simes is also unavailable, with last season's debutant Carter Hobbs returning and fellow batsman Daniel Burgess making his debut.
Taranaki import bowler Richard Clough was initially only going to play Whanganui's first game, but this weekend will get an opportunity to prove a point to his home association selectors.
After his debut for Whanganui was delayed, Hawke's Bay import Liam Hall has joined the team and is training well.
"He's a pretty quality seamer who bats. We'll use him in the middle order, and likely opening bowler," Marr said.
The rest of the side is the same as against Wairarapa – Ross Kinnerley, Chris Sharrock, Harpreet Binning and debutant Sam Roebuck, with one more to be added.
Taranaki had a strong start to their Furlong Cup campaign, picking up a first innings points win over Horowhenua-Kāpiti in a rain-affected game in Levin.
Veterans Bailey Wisnewski, Dean Robinson and Liam Muggeridge were among the runs as the whole team contributed to their 299-9 declared before they bowled out the home side for 172.
Play starts at 10.30am on Saturday and Sunday.
The Whanganui team is Greg Smith (c), Ross Kinnerley, Hadleigh O'Leary, Mark Fraser, Carter Hobbs, Liam Hall, Daniel Burgess, Chris Sharrock, Richard Clough, Harpreet Binning, Sam Roebuck, One TBC.
Whanganui's remaining Furlong Cup draw is:
November 12-13: vs Taranaki, New Plymouth
December 3-4: vs Manawatū, Victoria Park
December 10-11: vs Hawke's Bay, Napier
January 14-15: vs Horowhenua-Kāpiti, Levin
Six matches will be played for the second round of the Combined Twenty20 club competition at Tasman Tanning (Victoria) Park on Saturday.
Three games will start at 12.30pm and three at 3.30pm.
Draw for November 12 - Combined Twenty20
Kaitoke Knight Riders vs Wanganui Old Boys-Tech
Property Brokers Wanganui United 2nd XI vs Wanganui Vet Services Marist 2nd XI
Wicket Warriors Whanganui vs Property Brokers Wanganui United 3rds
Matt Burke Engineering Marton Saracens vs Kaitoke Knight Riders
Wanganui Renegades vs Wicket Warriors Whanganui
Wanganui Vet Services Marist 2nd XI vs Property Brokers Wanganui United 3rds
Bye: Hunterville Hackers