there was a discussion last year when williams was in great from that mcguire had make an inquest to see if he was interested in playing for the kiwis. So with that being said its likely he has some sort of NZ heritage.
There's a bigger game being played out at this week's 'Got A Trade?' NZRL National Youth Tournament in Rotorua.
www.scoop.co.nz
Selected in a team of Aus based Kiwis to play NZ based U18s side.
And also listed in this Kiwis article
New Zealand name wider World Cup squad ahead of 2022 campaign
www.weststigers.com.au
I can only find Sifa linking himself to Tonga though, not Samoa
From garbo to NRL enforcer: How reborn Sharks star bounced back from South Sydney sacking
www.foxsports.com.au
To answer your Royce question it looks like Aus, Kiwi or Somoa are all options so you'd assume he'd be a shot for Samoa depending on who else with mixed Islander heritages chose where. NZ you'd think would have to lose a few to Tonga/Samoa for him to come in.
Quick google didn't give me any answers if he may have played any junior reps.
So you are on to something. Sorry for continuing to discuss in the discussion thread like some kind of heathen.