The short answer is hard.
The longer answer involves advanced technological aids.
Jacob Schopf represented Germany at the 2020 Olympics in Tokyo, where he won a silver medal in the sport of canoe sprinting. The Olympic events for this sport include separate categories for men and women, singles and doubles, as well as distances of 1000 meters, 500 meters, and 200 meters.
This video from last year shows Schopf using a stationary simulator. I can't find much information about the simulator, aside from this video which shows how complicated it is to enter a kayak in it. Instagram user @CanoeSport illustrates a variety of exercise machines that appear to be made specifically for canoe sprinting.
-via Super Punch