The candidate's driver was killed in the initial burst of gunfire, but three police officers guarding them fought back and killed three of the attackers.
The candidate was wounded in the leg, he said.
"Our initial inquiry showed the attack was election-related," Goltiao said.
Goltiao said the largest Muslim separatist rebel group in the southern Philippines was known to be active in the area, but there were no indications the Moro Islamic Liberation Front was behind the ambush.
Since the election period began on January 14, national police said about 100 people have died in nearly 120 poll-related incidents of violence across the archipelago.
Thousands of political hopefuls were concluding their push for votes on Saturday.
About 15,000 police officers were put on alert on Friday to secure the polls.
Elections in the Philippines are often marred by cheating, vote-buying and violence, particularly at the local level.
Even before the votes have been cast, the left-wing group Bayan, which has candidates running for congress, called on the public to "prepare for mass protest actions against the expected massive fraud and violence".
About 45 million registered voters are due to cast their ballots on May 14 for 12 senators and 275 members of the House of Representatives, as well as hundreds of governors, mayors, and provincial and city councillors.
Nearly 87,000 candidates are standing for office, but the focus of attention has been on the race for a dozen seats in the 24-member Senate.
President Gloria Arroyo's handpicked Team Unity (TU) is being challenged by the Genuine Opposition (GO), a coalition backed by the deposed president Joseph Estrada, who is currently in jail facing corruption charges.
The TU senatorial candidates are due to hold a rally in a suburb of Manila on Saturday, while the GO held its main rally late on Friday.
The parties' candidates will continue to appeal for votes on Saturday until the campaign period officially ends at midnight.