Both All Black hopefuls made an immediate impact, with Fifita crossing over for Wellington's first try, while Coles' loose ball dive a few minutes after coming on led to a second half try.
Taranaki - who also surrendered the Ranfurly Shield to Waikato this season - will play in the Championship next season for the first time since its inception in 2011.
The bonus point win sealed Wellington's spot in the premiership semifinals.
Wellington 34 (Vaea Fifita, Teariki Ben-Nicholas, Matt Proctor, Malo Tuitama, Sitiveni Paongo tries; Jackson Garden-Bachop 2con, pen, Trent Renata con)
Taranaki 10 (Warwick Lahmert try; Beaudein Waaka con, pen)
Halftime: 12-10