I can't for the life of me figure out what a cavalry regiment would do with chaps, mind you ... and "issue" ones at that. Maybe they had members competing in the Calgary Stampede, and required them to be "in uniform"?
They were cold weather gear. I had a fellow send me photos of a pair and the local LdSH museum curator I think was stumped at first (this was several years ago) but our cavalry veteran knew them and had been issued them himself. He was 15th Alberta Light Horse in 1939 before going into The Calgary Highlanders and eventually fighting in Italy with PPCLI. The fur - buffalo hide? - was to keep you warm in the saddle. The horse would probably keep the back of your legs warm, I guess?