Hi nomi
I'm afraid I can't really advice on the best tactic concerning whether to adjust your insulin dose or go for the muching, it partly personal choice and partly I don't canoe..
But to prevent your insulin getting frozen, you can do one of two things, either stash it in the middle of a rucksack, so the contents act as an insulator, or keep it in a inside pocket near to the bodys as possible, it would also be a good idea to do this with your blood glucose meter and strips, these can grumble at being cold as well..
As to the conoeing and making your choice of action plan, I would consider the effects of your walking, against what actions of canoeing... Does walking, and using the big muscles in your legs, take more energy than the action of using to smaller muscles in your arms to paddle? How much is the adrinain (sp) rush canoeing going to effect your blood sugar levels, adding this into the factor may make a difference to what action plan you use..
what ever you choose, ensure that you take regular blood tests, partly to ensure you keep your self out of trouble, but also this will be your guide for the next time you go to build your action plan, I would also suggest regular BG testing after you've enjoyed yourself, so that you can build a picture of what changes you may need to make later on.. sometimes there is a time lag, between when you exercised and when it hits/impacts on the blood sugars..
I hope this is helpful and hopefully someone else might come along with experience of this, and give you more information