At least 30 people were wounded in the blast, which occurred just after the rally hosted by the JUI-F religious political party ended on Friday morning, said a police official, speaking on condition of anonymity.
Meanwhile, Sharif arrived in the eastern city of Lahore from London where he was visiting his ailing wife when a Pakistani court convicted him and his daughter of corruption.
The attacks came as authorities braced for the return and expected arrest of former prime minister Nawaz Sharif on a corruption conviction.
Police had earlier said that the attack targeted Raisani's convoy but later changed their statement as video footage of a large tent showing damage from the blast was circulated.
At least 128 people, including Raisani, were killed in the deadly blast, police officials said.
Durrani is running against cricketer-turned-politician Imran Khan, whose Pakistan Tehreek-e-Insaf party (PTI) is one of the front-runners in the July 25 vote.
There are fears of more violence in the run-up to polling day.
The explosion comes hours after four people were killed and 39 injured when a bomb hidden inside a motorcycle detonated near a Pakistani politician's convoy in the country's northwest on Friday, near the Afghan border.
The Islamic State group has a muted presence in Pakistan but has carried out brutal attacks there in the past, including the blast at a Sufi shrine in February previous year which killed almost 90 people. The bombing was the biggest attack in Pakistan in over a year and is the third incident of election-related violence this week.
Mr Durrani is running against popular former MP Imran Khan. On July 7, seven people were injured when a convoy of a Muttahida Majlis-i-Amal came under attack in Bannu.
The second explosion was in southwestern Baluchistan province, that killed 65 people and critically wounded the candidate.
Caretaker Chief Minister Dost Mohammad Khan condemned the incident and summoned an emergency meeting to discuss the security situation in the aftermath of the attack.
In a tweet, he said there seems to be a conspiracy to sabotage the vote. But he said the people of Pakistan will not allow anything to prevent "historic" elections from taking place.
On Tuesday, Awami National Party leader Haroon Bilour, among 22 others, was martyred in a suicide attack in Yakatoot neighbourhood of Peshawar.