The Department of State Services (DSS) arrested Kanu at a hotel in Lagos state, where he was lounging with a lady.
According to Soludo, the continued arrest of the IPOB leader will make him a hero or a martyr.
The CBN Governor also added that the Biafra agenda will not change, no matter how long he is detained.
Soludo to Buhari to release Kanu or else, the issue will be used to campaign against him when he seeks re-election in 2019.
He also cited an incident when the release of Chukwuemeka Ojukwu was used by Shehu Shagari to get people to support him.
Soludo said the current administration has made the IPOB leader popular by his detention, adding that he was unknown until he was picked up by the DSS.
One of the new IPOB splinter groups, the Reformed Indigenous People of Biafra (RE-IPOB), recently accused Nnamdi Kanu of using the Biafra struggleto enrich himself.