Tonga's Fifita set to hit top gear at RLWC

The prized back-rower's form at NRL level has fluctuated over his two-year stint at the Titans, but he underlined why the club spent so much money on him when he made his Tongan debut last weekend.

Fifita bagged a hat-trick in a 48-12 win over France in Halifax and will be critical to their hopes of going deep into the tournament.

"We've still got to figure out how to use him," Tonga coach Kristian Woolf told AAP, ahead of next week's tournament opener against Papua New Guinea.

"We've got an extremely powerful back row with Keaon Koloamatangi, Haumole Olakau'atu, Jason Taumalolo and Felise Kaufusi.

"What I will say about Dave is that I have been extremely impressed with him and the way he's fitted into camp.

"He's an exceptional athlete, he's got an ability most people don't.

"We've all got to be pulling in the same direction and David's going to be a big part of that."

Woolf said he didn't need to coerce Fifita into switching his allegiance from Australia to Tonga.

The Tonga coach said the forward had spoken to Kangaroos coach Mal Meninga, who also doubles as the Titans' performance boss, to explain his decision.

Tonga will be hoping to go one better than the 2017 tournament where they stunned New Zealand in the group stage and narrowly lost to England in the semi-finals.

The one question mark over a repeat would be the make-up of their halves.

Tui Lolohea is expected to partner St George Illawarra's Junior Amone - both of whom are traditional five-eighths - with Dolphins-bound playmaker Isaiya Katoa providing back-up.

"Tui's experience and previous performances with Tonga and what he's done for Huddersfield this year (have been great)," Woolf said.

"His fitness levels and the impact he had on their team, I think it's the most consistent year he has had.

"The other slot is up in the air, Isaiya is really talented and has impressed and Junior has done a great job for the Dragons and for us in the mid-season Test."