This isn't a definitive answer, but still might help.
As a Canadian, you will need to get an ETA to visit Australia -
All travellers, except New Zealand citizens, must obtain a visa or travel authority before travelling to Australia.
More information on the ETA is available here - http://www.immi.gov.au/visas/visitor/601/
Your ETA is valid for 12 months. You can enter and stay in Australia for up to three months at a time. If your passport expires before your ETA, you will need to reapply.
Your ETA lets you enter Australia for up to three months at a time as a tourist or for business.
You must comply with all ETA conditions and Australian laws. You cannot stay in Australia for longer than three months on each visit.
Nothing there seems to suggest that your visa does not reset when you leave the country, so a trip to NZ may suffice in allowing you to stay for 3 months in Australia on return from NZ.
There's some anecdotal evidence of this being allowed here (http://yanksdownunder.net/topic/8794417/1/) but I wouldn't bet on it.
I know the US doesn't look too kindly on this kind of behaviour for Australians though (i.e. Australian ESTA holders visiting Canada and returning to the US hoping for a visa reset).
I'd ask your local Australian embassy just to be on the safe side - http://www.immi.gov.au/contacts/visa-enquiries/eta.htm