Had half the day free in the area so decided to look what to do and so happy I did the canoeing! I would personally rank this about the pancake rocks themselves.
The price is pretty cheap (compared with kayak tours in NZ). 40NZD for 2h and 5NZD extra every additional hour. They provide you with a airtight container for your gadgets, wetsuit and shoes.
The scenery is beautiful! Like if you were in Jurassic Park. And you are by yourself all the time. You'll occasionally encounter some fellow travellers on the hiking track that goes alongside the river.
As you go upstream, the river will become more and more challenging. If you have continuous difficulties going through one part, I would say it is time to turn around as coming downstream if you don't control the canoe, it might capsize. However, the water is shallow so there is nothing to worry about. Part of the adventure!