This was the highlight of not only our Amsterdam visit, but our starting of a month Europe trip would not have been the same if we missed this activity.
I found Wetland Safari while watching a Rick Steve's Amsterdam special about two weeks before our arrival. I was shocked that it was so easy to book our event and so easily follow arrival directions for us novice European travelers. We were so fortunate to have Majel Tromp from the show be our guide and she was unbelievable. I'm not sure if she is the only guide or not but she was awesome!!
Don't worry about the strength for the boating activity; walking around Amsterdam city is more strenuous than the canoe rowing, so you will be fine. I personally wore swimming trunks to take advantage of jumping into the river at lunch which was beautiful (highly recommend doing the same). If you are looking at this site already... DO IT!! Your only regret will be that you didn't. Netherlands outside the city is spectacular. Good luck and have a blast!!! I would have paid tripled the price for this great adventure.