Although the organisation has not been formally set up, last summer they obtained a UK trademark for The Foundation of the Duke and Duchess of Sussex, suggesting it would be Britain-based.
At the time the couple's spokesman said a "full board and trustees will be appointed in due course".
However, tax experts in the US say they can exploit a number of commonly used loopholes to ensure wealthy Americans will still part with millions of dollars in donations.
One option the Sussexes could consider would be establishing an American-based "friends of" the charity.
The Prince of Wales and the Duke and Duchess of Cambridge, already have created such "friends of" organisations for The Prince of Wales's Charitable Foundation and The Royal Foundation of the Duke and Duchess of Cambridge.
The US affiliate of the Prince of Wales's charity took in £6.4 million (NZD$12.6million) in America last year, according to tax records. The Duke and Duchess of Cambridge's US branch raised $740,000, tax records show.
However, The Sunday Telegraph could find no public record in America to suggest the Sussexes have yet set up such an organisation.
Another solution would be for the Duchess to use her American citizenship to set up her own foundation or charity in the US.
The British and American versions could work together to support one another in a transatlantic partnership, potentially each fundraising and paying staff (including the Sussexes) in both countries.
Strategists have outlined a number of ways in which the couple could generate an income in the US or Canada, pointing out that their huge social media presence will be highly coveted by potential advertisers.
"I don't think they will do a straightforward charity, but something much more punchy," Sara McCorquodale, founder of influencer intelligence platform, CORQ, told CNN.
"I see them going down a Goop route," she said, referring to the lifestyle company founded by actress Gwyneth Paltrow and estimated to be worth $250 million.
Comparisons have also been drawn with the Obamas, who are paid hundreds of thousands of dollars for corporate speaking events.
But, the couple can find other ways of boosting their income. Before their shock announcement, both had secured roles outside the Royal family, with the Duchess' fee going to charity while Prince Harry's was unpaid.
The Duke worked with Oprah Winfrey, a guest at his 2018 wedding, on an forthcoming Apple TV+ documentary series about mental health for Apple.
He also told The Telegraph how he was "inspired" by his experience of telling his story about his struggles with mental health which had such a "impact" on others.
Meanwhile, the Duchess is reported to have signed already a voice-over deal with Disney in exchange for a donation to Elephants Without Borders, which helps protect the animals from poaching.
She could even resurrect The Tig, a lifestyle blog she wrote while living in Toronto which featured restaurant reviews and commentary on the latest fashions.
Despite shutting it down before her marriage, last year the trademark was renewed, alongside another for Tig Tots, a move Buckingham Palace said at the time was an attempt to prevent copycats.
When she launched her lifestyle blog, The Tig, she used a small web designer based in a unit in a shared warehouse near her home.
When it came time to make the "Sussex Royal" website she went back to the same designer. They have declined to comment on any other plans she and her husband may be drawing up that they are aware of.
Any return to Toronto would certainly bring them into contact with numerous well-connected friends who could become influential fundraisers.
The Duchess' close friendship with Canadian native and consultant Markus Anderson, dubbed the "King of Soho House", is well known.
Anderson's day job involves working on launches of various Soho House branches across the world, bringing him into contact with the rich and powerful.
Kirsty Young, the former host of BBC Radio 4's Desert Island Discs, whose husband Nick Jones, is the founder of Soho House, is a trusted friend of the Sussexes and was the first person the couple asked to join Sussex Royal.
For two years, until shortly before she met the Duke, the then Meghan Markle dated chef Cory Vitiello, who still owns a restaurant near her old home in Toronto, where she filmed Suits.Mr Vitiello, now a celebrity chef in Canada, has always declined to comment about the Duchess.
Along with Mr Vitiello she developed a connected social circle in the city which included her best friend, TV fashion stylist Jessica Mulroney, the daughter-in-law of Brian Mulroney, the former Canadian prime minister.
A short flight to Hollywood would allow them to meet the British actor James Corden, who also attended their wedding.
He has built up an enviable contacts book of American celebrity friends as host of The Late Late Show.
It would take very little for him to make introductions that would prove invaluable to a couple looking to promote their passion for charitable projects and campaigns that could inspire future generations.
If they do stay in Canada their popularity could possible open doors of a different kind. A recent poll for the National Post showed 61 per cent supported the idea of making the Duke the next Governor-general.
Another cost cutting perk came when Tim Hortons, Canada's biggest fast food chain, promised them free coffee for life if they set up home there.
However, if like former presidents, American actors and celebrated journalists, the Sussexes hope a charitable foundation is a way to secure a lasting legacy, they have a number of tried and tested formats that have proved hugely popular in America and Canada.
