@ OP - 100 cc wouldn't not be suitable to northern areas and as the height increases you will find yourself pushing the bike as it will refuse to go on. I had a friend who became adamant about travelling to lake saif al malook (in kaghan valley) on his cd70. He did manage to reach the lake but that you cannot say that he rode his cd70 there. At many places he had to drag the weight of his bike, especially around slopes.
So if you are looking to do a bike tour of northern areas where you sit on a bike then you should take minimum a 125cc bike. Else, if you plan to part-ride-your-bike and part-push-your-bike then even a cd70 will do the job.
I personally feel that the best bike for tours of northern areas in Honda CG125 because:
- it has the best power to weight ratio in today's locally available bikes
- it has the best spare parts and mechanic availability in northern areas
- it is extremely light weight and so very easy to maneuver around rough tracks
Before I get accused of being a cg125 fan, you should know that I own a cg125, a gs150 and gs500. And I have also done many trips. I feel that a trail bike is best suited for such areas, but since such bikes are not yet available locally (fingers crossed for qingqi) , the best bike for now is cg125 (for reasons stated above).