In your case Taupo Air Canada would make more money if you book it on AC.com as an AC number.

In general, a code share distribution just means that the selling airline gets a commission on the ticket that they sold on the other airlines metal (not medal). First of all the revenues will be split by a pro-ration based upon the ratio of mileages of each sector.

If the ticket is booked on NZ's site then NZ gets a commission on the AC sector and NZ keeps all of the money for their own sector.
If booked on AC.com then AC keeps everything for their sector and gets a commissiom for the NZ sector.

The primary idea behind a codeshare is that it increases the display of an airlines own sectors and the display leads to a sale on their own flights that they might not have gained otherwise. In the case of YVR-AKL, without the codeshare the buyer might have gone to another airline for the transborder sector.