I have done a lot of canoe camping over the years. There is a circuit of lakes in BC called the Bowron Lake chain which I have done 3 times. It took us about 6 days to do the 70+ miles at a reasonably leisurely pace each time. There are numerous portages on this trip, and you definitely need to pay attention to weight. I agree with Dtape that the same lightweight backpacking techniques work well. When you portage all your gear, you will be glad of every ounce you saved.
I still remember seeing a scout troop struggling along with large sacks of canned food. Poor kids! Also, when doing the fast water stretches, if you pack light, you will have a little more free-board for peace of mind and better maneuverbility. We also usually take a heavy first night meal ..it breaks the monotony farther on. Put the beer and steaks in the other guys pack!