The opposition’s two strongest candidates have begun a two-day poll starting Monday to decide which of them should run in the Seoul mayoral by-election on April 7 to defeat the ruling party.

Oh Se-hoon of the main opposition People Power Party and Ahn Cheol-soo of the minor opposition People’s Party will conduct surveys of 1,600 people each, and add up the results to be announced by Wednesday. Should they be able to finish earlier, the final candidate may also be revealed on Tuesday.

The two failed to unify their candidacy by their initial deadline of March 19, but agreed that one of them has to give up running before the official campaign period begins this Thursday.

Pollsters chosen by the two parties -- Korea Research and Global Research -- will each ask 800 people who they think is suitable for the job, and another 800 people who has more “competitive power” by calling mobile phone numbers extracted by the national election watchdog.

For those who select “I don’t know” as an answer, they will be prompted with the same question and choice of answers again.

Poll results on Sunday showed that both Oh and Ahn can win the ruling Democratic Party’s Park Young-sun by a huge margin in a hypothetical two-way race.

In a poll of 1,006 adults in the Seoul region conducted by three pollsters and commissioned by three terrestrial broadcasters -- KBS, MBC and SBS -- 34.4 percent of those surveyed said Oh was more suitable, and 34.3 percent said Ahn was more suitable.

As for who has more competitive power against Park, Oh had a 39 percent support, and Ahn with 37.3 percent, the difference of which were within the margin of error.

In a hypothetical two-way race between Oh and Park, 47 percent said they would vote for Oh, versus 30.4 percent for Park.

Between Ahn and Park, 45.9 percent said they would vote for Ahn, versus 29.9 percent for Park.

On Monday, former Seoul mayor Oh was canvassing in the southeastern districts of Gangnam-gu and Seocho-gu, which are considered traditional strongholds of the conservative People Power Party.

He visited startup companies and child care centers in the morning, and was to walk from Yeongdong Traditional Market to Gangnam subway station.

Entrepreneur-turned-politician Ahn attended a meeting of his party’s supreme council, and was scheduled to move to Jongno-gu to sign a policy agreement with a civic group.

By Kim So-hyun (sophie@heraldcorp.com)