Their move comes amid growing concerns for who will pick up the bill for the couple's security once they leave their roles as senior royals.
Round-the-clock security, which could cost up to A$1.9 million a year, would be provided by the Metropolitan Police and paid for by UK taxpayers under their plan, however that may not be the case going forward.
According to a 1973 United Nations convention, internationally protected people include heads of state – such as the Queen – prime ministers, foreign ministers and diplomats.
But they also include anyone who officially represents a head of state, such as senior members of the royal family.
However with Harry and Meghan's new roles currently up for discussion, the level of protection they receive - or the level that is paid for from the Crown purse - could change.
A senior police source told the Evening Standard that "as the circumstances have changed there will now be a full review."
“Royal Protection by armed Metropolitan Police officers is mandated by the Home Office,” the Scotland Yard source said.
“Until now their official roles mean the Duke and Duchess of Sussex and their son are classified as internationally protected people. That stays in place for now. But as the circumstances have changed there will now be a full review.
“If the Sussexes intend to live abroad, and not just carry out international official visits abroad, it will involve far more resources.
“This will have to be reviewed and signed off by the Commissioner. There is no guarantee it will be granted.”
After Queen Elizabeth released a statement on Monday saying the final decisions about her grandson’s future role in the royal family will be made in “coming days”, Canadian Prime Minister Justin Trudeau on Tuesday confirmed his government was now involved in the negotiations.
He has reportedly promised the Queen that Canada will help pay for the young couple’s security, though finance minister Bill Morneau was less committal on Monday.
“We obviously are always looking to make sure, as a member of the Commonwealth, we play a role. (But) we have not had any discussions on that subject at this time,” he told reporters.