An article from a few years ago compared cross-country skiing and Nordic walking. Cross-country skiers invented Nordic walking so they could keep working out when there was no snow. 

Cross-country skiing is certainly the more taxing of the 2 activities, but there are ways to increase the intensity of Nordic walking. For example, turning your Nordic walking route into a circuit with different bodyweight exerciseslike pushups, planks, and lunges can get your heart rate up in no time.

Cross-country skiing	Nordic walking
Exceptional cardio-vascular workout	Excellent but lower intensity
Heavy upper body involvement	Full engagement of the upper body
Less beginner-friendly; must master skiing	More beginner-friendly
Low impact but terrain may be rough	Low impact on more hospitable terrain
Higher intensity for more fat-burning	Lower intensity but upper body involvement increases fat-burning over regular walking