Here is an interesting link with some videos of indoor training. Scroll down to see the videos of Daniele Molmenti demonstrating exercises he does indoors and a Chinese athlete demonstrating use of a swiss ball for indoor training.

http://canoeicf.com/icf/Aboutoursport/Canoe-Slalom/Canoe-Slalom-Development-Program.html

Scroll down through the page for the videos of indoor training.