"They suggested a lot of the activity we talk about hadn't really been demonstrated," he said.
"So Sunday is all about demonstrating what can be done and it's quite important that we get our message across to show people."
Grant was "very pleased" with the contribution from the Whanganui Community Foundation to what will be a regional facility and was now waiting to get a $6 million Government contribution confirmed.
Just months before coming Prime Minister last year, Jacinda Ardern committed to the $6 million grant, originally pledged by the previous National Government, if elected.
"She said in no uncertain terms the money was locked in," Grant said.
The group has been talking to Finance Minister Grant Robertson to set up a meeting and Grant was hoping for a Government announcement early next year.
"We just want to progress that because, I guess, it's like a domino effect. If we can get the contribution from the Government then we will attract a whole lot of others."
Grant said about $3 million of the $12 million needed had been raised, not including the Government's expected contribution.