Anybody who can walk, can walk with snowshoes. (With shallow snow, flat ground...)
On the other hand a heavy pack with slippery slush on a 40 degree slope and buried rocks and willows to posthole into it's a different story. (The North Fork of Lone Pine Creek on Whitney last weekend for example)
I trained with walking lunges to help condition my hip flexors. Going up stairs with ankle weights would be good too (elevator down or take off the ankle weights if you're walking). Double-unders with a jumprope (if you have enough rhythm), squats, burpees, all good.