Papua New Guinea won gold in the inaugural Championship in 2014, which was run as an exhibition event alongside the Glasgow Commonwealth Games.
Hunters player Stanton Albert was named player of the tournament as PNG went through unbeaten, defeating Australia 22-8 in the final.
The age restriction for the 2018 Championship has been increased from Under 19s to Under 23s.
Hosts Australia, defending champions PNG England and South Africa are confirmed entrants, with 8-12 expected to participate when the Championship in held in Brisbane in February.
