Find Your Cruise
Both Celebrity and Royal Caribbean offer cruises from Sydney to Auckland [either one way or round trip] If you want to do more then why not pick up the ship in Vancouver and cruise via Honalulu and Auckland to Sydney.
There is always the option of a liner voyage you can fly to or back from sydney then cruise from or too southampton, therefore only flying one way, the cruise duration is longer but you also get the chance to see many other ports you may not have done. Both Cunard and P&O do these journeys.
And if you are over 50 Saga does a RTW trip to.