Heres a related one: More elite rowers switch to elite cycling and vice versa than to/from rowing to any other water sport like canoeing because they're both mostly driven from the legs and demand the same cardio training routines. Its virtually unheard of for an elite rower to become an elite canoeist or vice versa.
Canoeing is very much different from rowing.
Canoeing is done kneeling on the canoe, legs only used for balance.
Kayak, which is very different from canoeing is done sitting down, again, no leg power used.
In rowing most of the power comes from the legs, thanks to the sliding seat.
Also, in rowing all the rear cynetic muscle chain is used, in canoeing and kayak mostly front.
In other words, it would be almost impossible for a rower to win an Olympic in canoeing/kayak.
But you're right when you say that rowers are also good cyclists, thanks to the legs power and resistance.
I have switched to mountain biking having had problems with my back because of 12 years of rowing and I keep up with bikers who have done that all their life, even much younger ones.
Rowers have mental strength on their side.