Fiji beat Tonga 8-nil in their last pool match at the Fiji Rugby Union Oceania competition in Lautoka last night.
Both sides will meet again in the final on Friday at the same venue.
The score was tied at nil all at halftime with hooker Josaia Vikaitonga scoring the only try and Kin Muri a penalty.
In other results Vanuatu beat Tahiti 29-19 and Samoa beat Papua New Guinea 33-5 in a friendly.
Meanwhile, Vanuatu and Papua New Guinea will play off in a two tier final with the winner heading to the International Rugby Board's under 19 junior world trophy championships in Poland.
Samoa will round off the competition with a friendly against Tahiti.