Brothers I have both cg125 and GS150 at my home. Let me be very clear that GS150 is better than cg125 in all aspects. But if you are thinking of touring whole Pakistan and you are not a very technically sound person then get CG125. You will be able to find its mechanics and spare parts at maximum places in Pakistan. Few months ago my GS150 had a leaky fuel filter. The nearest shop that had it in stock was at Mclore road. And this I am talking about Lahore. So just imagine what will happen if God forbid you need a spare part say on GT road or at Indus Highway or at Northern Areas or at some small town??
But if you know mechanics of bikes and can repair it yourself and DIY where ever needed then GS150 is the bike to take on such tours. It has a rock solid engine and is very, very comfortable.
Personally I prefer taking CG125 to long trips simply because I do not know much about bike mechanics. So I have peace of mind that I can find parts and mechanics at maximum places in Pakistan. I think even road side puncture walas can, to some extent, work on a CG125.