An example is swimming to stay in shape for snowshoeing. Although swimming will keep your cardiovascular fitness high, it will not help your body to deal with the specific demands of snowshoeing. Nothing can fully replace your individual sport for getting you into shape. And by this I mean real stairs, not the indoor machine version. Stairs don't give when you push down, they offer full resistance.
Real stairs require full body balance, an important element of many winter sports.
Real stairs are not nearly as boring. Try to find a flight of stairs in the 200-400 step range for the best interval. An outdoor stadium is excellent. Go hard on the uphill and easy on the down - the essence of interval training. Vary your stride length - one stair at a time on one set and two at a time on another set.