apple watch 3 cellular support in pakistan?

I would recommend that Pakistan users do not buy from the online shopping sites you linked above. There is no guarantee they will be selling a version with LTE bands compatible with Pakistani networks, and they will be black market imports so no warranty or support.

The list of worldwide carriers supporting Apple Watch with cellular is online at Apple Watch - Carriers - Apple. There is no cellular support yet for Apple Watch in Pakistan.

http://www.shophive.com/apple/watch/series-iii

Scroll to the bottom of this link....call them and ask where you can get support......Apple Smart Watch Series 3 Prices in Pakistan | iShopping.pk