The military presence is just the latest controversy in a bitter campaign season that has seen accusations of "pre-poll rigging", the expansion of hard-line religious parties, and a string of bloody militant attacks that have killed more than 180 people, including three candidates.
Later Sunday, the Pakistani Taliban claimed responsibility for the suicide bombing that killed Gandapur.
On the other hand, several surveys carried out by national and global organizations show PTI leading the political battle followed by Pakistan Muslim League Nawaz and Pakistan People's Party.
After his younger brother's death, Gandapur was elected as a member of the assembly of Khyber Pakhtunkhwa province and appointed provincial minister for agriculture.
The election campaign has been marred by terrorist attacks and allegations the military is working behind the scenes to support Mr. Khan, who has aspired to lead the country for two decades. "Either it is Pakistan Tehreek-i-Insaf or Pakistan Muslim League-Nawaz, there is many a slip between the cup and the lip", he told PTI.
Critics have long accused Pakistan's powerful military, including its Inter Services Intelligence (ISI) agency, of meddling in politics and judicial affairs, a charge it denies. After the results, 27 winning independent candidates joined Sharif's party to give it a majority.More news: At least 11 dead, 7 injured in Missouri duck boat accident
Pakistan's army has said it will deploy more than 370,000 troops on polling day - around five times as many as for the 2013 poll when the country's security was generally considered to be much worse.
Shehbaz has been named as the prime minister-designate if his party wins the July 25 general election.
Shehbaz said that Pakistan can not become a great nation by voting leaders like Imran Khan who have made false promises to "our nation".
During Pakistan Election 2018, 53,000 local, national, and global media observers will monitor the polls.
BehindYouSkipper became one of the country's top trending hashtags as celebrities and former cricketers came to Khan's support.
The Pakistan Peoples Party of Bilawal Bhutto Zardari - son of murdered premier Benazir Bhutto - could become kingmaker by forming a coalition with one of its rivals.