If I could read "Auckland" in your little profile box I suppose that would help. Apologies about the obliviousness.
I haven't done much boating around Auckland. From what I gather there is some stuff to do, and some of it is easy and some is still super hard (Tuakopai River). It didn't rain enough while I was there to get on anything in that area and I headed off to the South Island. You could always contact some of the Blisstick boys and see what they have to say. They were super helpful in giving me info when I was looking for it.
Here is what New Zealand Whitewater by Graham Charles says about the area. This is more for kayakers but still decent info:
Introducing the northern North Island in a classic whitewater guide is a bit like introducing places to sunbathe in Antarctica in a classic resorts book. The northern regions are best left for sea kayaking, diving, fishing, and sitting in traffic jams.
But if you insist- the best (and only) time to go paddling in Northland is after solid rain. The Mangakahia (near Whangarei, from the bridge on Kaikohe-Donnelly's Crossing road) and the Wairua make up the Northland river options.
South of Auckland the Waitetuna (near Raglan), Waitahweta (tributary to the Ohinemuri) and possibly even the Pokaiwhenua (near Arapuni) may dish up some interesting water if you get the flows right.
Karangahake Gorge is the closest whitewater of significance for Auckland paddlers and is worth a visit if you are in the area and it has rained enough.
If you are really stuck in the north end and need a good pounding in your kayak do what the locals do and head to the surf. Raglan has one of the best breaks in the world, and in the far north there are beaches galore.
You could also contact some of the guide services on the Kaituna. I know they do commercial rafting there and I'm sure they'd be happy to give you some beta.
Hope that helps! Cheers!