Entrepreneur and billionaire Sir Richard Branson says cannabis could replace New Zealand's reliance on cows if the drug was legal.

The entrepreneur, who was in New Zealand at the weekend for a charity dinner, told Newshub's Samantha Hayes the war on drugs was an abject failure.

He said there was a big business opportunity for New Zealand-grown marijuana.

It is illegal to grow, import, sell, possess, and use cannabis in New Zealand.

Branson said Kiwi farmers could have a new venture, cannabis over cows.

"You should legalise it, grow it, tax it, regulate it.

REUTERS/JASON REED Virgin Group founder Richard Branson said cannabis could replace cows if the drug was legal in New Zealand.

"I think that would be wonderful because obviously the amount of dairy cows that New Zealand has is damaging the rivers, if you could put some of that land over into growing cannabis would be just as profitable for them, if not more profitable."

Federated Farmers national president William Rolleston told Newshub he was not opposed to the idea.

"Farmers welcome any opportunity to add another string to their bow and would look at that option if it was legal and profitable to do so."

Meanwhile, legislation will be introduced in Canada next month proposing legalising marijuana by 2018, the country's media reports.

The Liberal government led by Justin Trudeau is expected to announce a federal bill to allow the sale of marijuana by Canada Day, on July 1, 2018.

CBC News reports the legislation will follow recommendations by a federal task force charged with investigating the necessary framework and health considerations if cannabis were legal.

TRISH BADGER Canada's Prime Minister Justin Trudeau's Liberal government is tipped to announce legislation proposing the legalisation of cannabis.

In Canada, the drug is classed as an illegal controlled substance but can be supplied in some cases for medical use.

The report said a police chief briefed the Liberal caucus on the roll-out plan for the legislation.

According to the report, the federal government will control supply of the drug including licensing, but Canadian provinces will be able to decide how the drug is distributed, sold, and priced.

Ottawa, the federal capital, will set a minimum age of 18 but this could be increased at provincial level, the report said.