"Reaching/Lunging/Bending" is soooo 1990's!
Mr Paddleshop hit the nail on the head with regards to boat dynamics. You need to let the boat glide with you, and you've got to ensure the boat does her fair share of the work. If you lunge then you're throwing a good proportion of your weight forward and you drive the nose of the boat into the water, causing extra drag and reducing that gliiiide.
Secondly, if you think about what muscles you want to work: the biggest! Therefore you need to be using your legs, abs and lats. These large muscle groups are super strong and can go on and on and on, so we need to make the best use of them. As you lunge forward, yes you are getting a good long reach, but as you straighten, you are engaging your lower back muscles. These puny muscles tire very quickly in comparison to the Big Boys. If you twist and as you get that first catch you're using more abs and lats.
If you want proof about body weight, look at any of the olympic canoeists videos and see where their body weight is in comparison to the centre of the boat. And you'll have your answers.