Eventually, PIA Boeing 777-200LR aircraft registration AP-BGZ left Islamabad as flight PK781 to Toronto at 10:05 PM with a delay of 7 hours & 50 minutes.
Flight PK781 to Toronto was scheduled to leave Islamabad at 2:15 PM. The aircraft (AP-BGZ) had arrived in Islamabad at 10:51 AM as flight PK782 from Toronto.

Source: flightradar24.com
Flight PK781 information on Islamabad Airport website:

Source: islamabadairport.com.pk
Abbas