Mr Cunliffe said he hoped to do the Campbell Live gig but was still in discussions with the broadcaster over a suitable date.
Having previously said he was hoping New Zealanders would get to know him better, he said he was not trying to avoid pieces that touched on his personal life. "I'm looking forward to it."
He said the first scheduled date had to be cancelled because of a family illness. There was a misunderstanding over a second night which Campbell Live believed was confirmed but Mr Cunliffe's office did not and had a diary conflict.
John Campbell, host of Campbell Live. Photo / Doug Sherring
He said he had put some thought into accepting today's speech invite because it was a sitting day.
"We carefully weighed up the balance between the opportunity to ask questions today and the need to really speak to this very large and influential audience. We went with the audience, in consultation with the IOD and I consulted my senior team on it. We thought it was the priority for the day and I'll be back in question time all guns blazing tomorrow."
Mr Key said the decision not to attend question time was "odd" given it was just before a two week recess and one of the few opportunities to tackle him head on.
"This is the place we debate big issues. This is the his chance to take me on. As leader of the opposition one of the best places to hold the Government to account is in Parliament."
He was also surprised Campbell Live was having trouble getting Mr Cunliffe for the dinner with the leaders, saying such pieces were good for the profile of any political leader.
Mr Cunliffe also said Mr Key had agreed to speak at the same event in Auckland but had pulled out and made Steven Joyce do it instead.
Mr Key's office denied that, saying he had been invited but had turned it down because it was a sitting day when Mr Key was usually in Parliament for caucus and Question Time.