Debate organiser Shayne Jeffares said he was planning an "old town hall style" format where Mr Nash and Mr Barker would talk for about 15 minutes each, followed by a time for questions.
The debate will be held at the Photographers' Gallery, formerly the Red Cross Hall, on Tennyson St, at 5.30pm on Friday.
There will be a $5 door charge with the proceeds going to charity.
The debate is happening on the same day that submissions close on the Local Government Commission's draft proposal on the amalgamation plan it has put forward.
Commissioners are expected in the region next month to hear in-person feedback on the proposal, which has drawn strong opposition from many, especially in Napier, Wairoa and Central Hawke's Bay.
A public meeting in Waipawa last month, where Hastings Mayor and amalgamation supporter Lawrence Yule squared off against anti-amalgamation campaigner and Napier Mayor Bill Dalton, drew a crowd of about 200.