I've just phoned the NZ national reservation centres for Hertz, Budget and Avis regarding licence requirements. A full, current Canadian licence which you have held for more than 12 months is fine.

Re traffic issues - once you get to the fantastic South Island with its 15 miles of motorways, I don't think you'll have much of a problem! Remember to ask at the rental counter if they have any discount books, deals on FF points, etc. I used to work for Hertz and they had coupon books that give you discounts on most visitor attractions around NZ.

And as for fog lights - maybe shillard accidentally joined the Rally of NZ!