Shehbaz has been named as the prime minister-designate if his party wins the July 25 general election.
Earlier, PTI Chief Imran Khan took to Twitter to condemn the "cowardly terrorist attack".
The upcoming elections have largely been a race between two main players-former Prime Minister Nawaz Sharif's Pakistan Muslim League (N) (PML-N) and cricketer-turned-politician Imran Khan's Pakistan Tehreek-e-Insaf (PTI).
The attack followed a suicide blast in the southwestern province of Balochistan on July 13 which killed 149 people, underscoring continuing security challenges in Pakistan following years of dramatic improvements.
Responding to the MML contesting Pakistan general elections, the USA state department recently said, "We have repeatedly expressed our concerns to the Pakistani government about LeT, including the participation of LeT-affiliated individuals in the elections".
At least 10 kg of explosive material was used to target the vehicle, District Police Officer (DPO) Zahoor Khan Afridi said, as he confirmed the deaths of Gandapur and his driver.
On the other hand, the election for PK-99 has been postponed, the Election Commission announced shortly after Gandapur was killed with his driver in a bomb blast near their auto in Dera Ismail Khan Sunday.
Victim's girlfriend says gunman provoked fatal 'stand your ground' shooting
McGlockton's family tells ABC Action News they plan to hire their own criminal attorney to look into this case. A sign posted outside Drejka's home Friday said: "No Comment" in bolded letters.
A suicide bomber blew himself up near the vehicle of Gandapur as he left his house for election campaign.
The Pakistani Taliban claimed responsibility for the attack, a spokesman for the militant group said.
On Saturday a Pakistani anti-narcotics court jailed for life Hanif Abbasi, an aide of Sharif, for misuse of a drug-making chemical, a government prosecutor said.
The PML-N alleges that its candidates and supporters have been urged to switch loyalties by people identifying themselves as intelligence or military officers across the country. This poll has created a do-or-die situation for the incumbent party, which is now being helmed by Nawaz Sharif's brother, Shehbaz.
A frustrated PPP leader Farhatullah Babar was quoted by newspapers in Pakistan as saying, "Seldom before has the pre-poll process been so vitiated, so unfair and so grotesqueThe invisible political engineers seem desperate for a fragmented and divided parliament that is easier to manipulate".
The nation has been on edge over Wednesday's elections that will decide Pakistan's new prime minister after a string of similar suicide bombings this month against political candidates. "No one can doubt your Honesty and thats what is require in our country.An honest LEADER", tweeted former captain Waqar Younis.