There are a number of routes but none are easy.
1. Heading out of NZ due east staying between 35-40 south. Your destination would be the southern Cook Islands. Plan for a rough trip with lots of wind shifts as the fronts pass you. From the Cooks head north to Tahiti, then Christmas island (Kiribati), Hawaii and then over the top of the high to the west coast.
2. NZ due north via Samoa, Kiribati, Midway and then north until above 48 finally turning east.
3. NZ north via Japan and then circle route to the west coast
4. NZ to Kiribati then east along the counter current till you reach Christmas Island and then head north. Plan on lots of motoring and bring extra fuel. We have good friends that did this in a Tri from Ponepae.
5. Heading around to the West as the previous post mentioned
6. NZ direct to Hawaii. Closed hauled the whole way. We have a friend that did that in a Wylie 28. One tack till 80 miles from Hawaii then flopped over. Mostly all upwind.
All of these are long. But a number of folks do that trip every year so there should be folks out there that can give you first hand experience.
You may want to pick up a copy of Cornell's WORLD CRUISING ROUTES
. Good info