The all-rounder made 86, with Corne Bodenstein adding 47 from 30 balls as Jersey batted first and were bowled out for 255 in the 48th over.
Vanuatu never got going in reply, Stevens taking 3-28 as they fell a long way short of the target.
Both finalists will be promoted to World League 4 next year.
Guernsey finished the tournament in sixth place after losing their play-off with Germany by four wickets.
Photo ICC. Caption: Vanuatu cricket team
