Though walking will give your legs an element of conditioning and increase your tissue load tolerance, it’s not going to give you the sport-specific strengthening that’s directly transferable to running and cycling. Hilly hiking will give your legs more general strength, but certain other muscle groups (e.g. hamstrings and glutes) need separate attention as they’re challenged more in running and cycling.
Your core won’t receive much strengthening, so this is something that would require specific exercises, progressing them as your control improves. Walking with a backpack over challenging terrain will help to some degree, yet because you always have one foot on the ground it’s not that functionally transferable to running and cycling.
There’s plenty evidence to suggest that having good, functional core strength and control equals a lower rate of injury in the peripheral joints, so make sure you do directed work for this. The key for strengthening and performance is to try to make your training as specific as possible to the activity, so aim to incorporate specific drills for each discipline.