The Kangaroos coach stopped short of guaranteeing the No.7 of the winning Origin team would claim the jersey at the World Cup, which kicks off at Allianz Stadium in 100 days' time.
But Queensland legend Walters will watch with interest on Wednesday night as NSW halfback Cleary fights to win a game-three decider on his fourth attempt.
Cleary started at halfback in all three games of last year's Ashes whitewash and steered the Kangaroos to glory at the last World Cup in 2022.
Uncapped at international level, interstate rival Walker won man-of-the-match honours in Origin II and was the Maroons' best in the series opener.
"Nathan's been our number one halfback for a long time now and rightly so, but also Sam is challenging, isn't he?" Walters said.
"Sam has made some huge strides since Origin started. He's been tremendous.
"The Origin tomorrow night will have a big indication on some players and whether they get selected in the Kangaroos, for sure."
Walters will factor in the incumbency of four-time premiership winner Cleary and also consider form in the NRL finals series.
Walker's Sydney Roosters and Cleary's Penrith are both in the top four heading into round 19 and have been tipped for deep runs this September.
"Obviously Origin's important but history in that Kangaroos jersey is important as well, as well as the finals series," Walters said.
"If someone jumps out of the ground through the finals series, that nearly automatically puts them into the Kangaroos selection frame."
Walters said on his Inside Ball podcast Brisbane's Reece Walsh would retain the fullback jersey at the World Cup after shining in the Ashes last year.
The 23-year-old was selected on the back of the Broncos' stellar run to the premiership that earned him the Clive Churchill Medal in the grand-final win over Melbourne.
He has failed to reach those heights this season for the 16th-placed Broncos.
But ex-Brisbane coach Walters said on Tuesday he remained a "big fan" of Walsh, his fullback in the 2023 NRL grand final.
"Obviously it's still 100 days away from the (first) game so there's a lot of football to be played, but Reece was outstanding last year in the fullback role," Walters said.
"He's got a good attitude and respect towards the Kangaroos jumper, which I'm a big fan of as well."
