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since i am NOT from Pakistan so obviously i haven’t done that but i have taken american airlines from toronto to delhi via chicago on American Airlines [AA] they have a non-stop flight to and fro ORD. its a long haul flight…16 hours.
the IATA rules are…if u have been ticketed in north america u are entitled to carry two checked in bags each not weighing more than 50 pounds [used to be 70 lbs] each and a carry-on bad weighing not more than 20 kgs [44 pounds roughly]. AA are pertty liberal on international routes.
there is PIA flight between delhi and lahore but not to ISB.
good luck and check with:
Cheap Flights, Airline Tickets, Hotels, Travel Deals - Search 1000’s of Travel Sites at KAYAK
they search almost all the airlines and give u a pretty good choice.**