The prime minister visited a Buddhist temple in outer Melbourne and later an AFL game, where he revealed the news two Australians had died in the terrorist attacks in Sri Lanka.

Opposition Leader Bill Shorten was in Cairns where he pledged to tear up a controversial $444 million grant the Turnbull government handed to the Great Barrier Reef Foundation.

But both leaders faced questions about the $80 million taxpayer-funded water buyback from two farms in 2017.

Australian National University water economics expert, Professor Quentin Grafton, said the $2745 per megalitre forked out by taxpayers in 2017 was about twice as much as should have been paid.

"So if you add it all up it's about $40 million more," Prof Grafton told Sky News on Monday.

Mr Morrison said the company's original asking price had been more than $5000 a megalitre, much higher than the agreed price.

He was satisfied former water minister Barnaby Joyce and Energy Minister Angus Taylor did not have a case to answer for any involvement in the deal.

"These arrangements were conducted at complete arm's length from any ministers," Mr Morrison told reporters in Melbourne.

Labor is waiting to hear back from the Agriculture Department before deciding whether to back calls for a royal commission into the water purchase.

"It matters whether or not this was value for money. It matters that it wasn't done through a tender process," Labor frontbencher Tony Burke told reporters.

Greens leader Richard Di Natale is demanding a royal commission into the management of the basin plan after questions about the buyback resurfaced.

"It verges on corruption and that's why we do need to see a full-throated investigation," he told ABC Radio National on Monday.

Mr Morrison campaigned in Jason Wood's seat of La Trobe, as he continued his bid to shore up Liberal seats around the nation.

He announced $15 million to back multicultural communities to start new businesses and support elderly migrants getting access aged care services.

Mr Morrison told a crowd at the Pakenham Lions football club about curries he made, and how it was a perfect metaphor for multicultural Australia.

"It all blends and you get the garam masala in the end - you know what I'm talking about. It's so good. It's so good. That's multiculturalism in Australia," he said.

Labor also went after the migrant vote, promising Long Stay Parent visas to allow more migrants' parents to get visas to see their children and grandchildren.

Mr Shorten said ending the 15,000 person yearly cap on parent visas would end the current "cruel" system, but the coalition warned the move would be unsustainable.

The Labor leader was in LNP MP Warren Entsch's seat of Leichhardt, where he promised to take immediate action to lift wages if he wins the election.

Mr Shorten has promised to reverse the Fair Work Commission's decision to cut some penalty rates within 100 days of taking office.

He was also asked five times whether he would review the Adani coal mine's approvals if Labor wins office - Mr Shorten did not rule it out but said he had "no plans" to do so.

Australian Associated Press