A police investigation was ongoing.
Cornwall Park Trust Board director Michael Ayrton said the fire caused significant damage to the cafe, which had been due to open on November 7 after two years of planning and construction.
The trust board had spent nearly $1 million on the cafe, which it hoped would generate revenue this summer to help with park maintenance, he said.
"I understand our leasee Andrew Bell was in the process of interviewing people which is pretty unfortunate, but he hopes to be able to be able to utilise them elsewhere.
"I know he had a baker lined up and some summer staff but I'm not sure exactly where he got to with that."
News of the fire had attracted an outpouring of sympathy from the public, Mr Ayrton said.
"We obviously appreciate the support we've had from the public and friends of the park and we're working closely with police and the community to get things back up and running as quickly as possible.
"A lot of people were looking forward to enjoying the facility over the summer, along with ourselves."
The park received nearly four million visitors a year, with a spike in numbers during the summer months, he said.
"It's just really unfortunate that it's going to be some time before we get some temporary facilities in place."
A food caravan and ice cream trailer would fill the void in the interim and the trust board had been considering opening a pop-up restaurant, he said.
It would take at least six months to rebuild the cafe, Mr Ayrton said.
In September, the board appointed Mr Bell to operate the new cafe, and the former Cornwall Park Restaurant, known as the Kiosk, which is closed for renovations.
Mr Bell referred enquiries back to Mr Ayrton.
