Gatland's men will be looking for revenge in Hamilton following their defeat to the same opposition in France four years ago.
But it will be no easy task after 27 European-based Fijians confirmed their availability for the global gathering.
Fiji assistant coach Shannon Fraser met with players at 16 clubs in Britain, Ireland and France during a trip to Europe.
All players spoken to had "expressed genuine interest in being considered and have communicated their availability," said Shannon.
That means Wales could face the likes of Scarlets prop and Fiji skipper Deacon Manu, Leinster full back Isa Nacewa, Toulouse wing Vilimoni Delasau and Castres centre Seremaia Bai in five months time.
Traditionally, the Fijian Rugby Union has struggled to persuade all its very best talent to appear for the country on a regular basis due to club commitments.
However, FRU High Performance Unit manager Talemo Waqa has been impressed with the attitude of Fiji's big names after it was left to individuals to clarify their intentions and resolve any contractual difficulties.
"While many people will love to see Nacewa and other top players released for national duties, the onus was with the players to sort it out with their respective clubs and see what's best for them," explained Waqa.