The best advice I can give you is to join Air Canada Aeroplan for free, login to their website and then use their award availability tool (working on the assumption that their availability is the same as UA's).

The annoying thing about that tool is that you can only search for return flights, not one way, and if there are not flights available in *both* directions it will come back with nothing. So, the thing to do is search for AKL-NRT-AKL dates waay in the future and find a pair of dates with availability for both outbound and return, and then change your outbound date for the dates you actually want to search - that way you know it will display the options if there are any.

Searching NRT-LHR may be a bit more tricky, as an annoying glitch in AC's award system is that if both locations are served by AC it looks for AC availability rather than *A availability, even though it makes no sense to route NRT-YVR-LHR (well, not if no miles are being earned, anyway ).

Good luck!