Harry is not a citizen neither of Canada nor of New Zealand and, unless he held a Crown office in those countries, or was an accredited UK diplomat there, what kind of representation role would he have there exactly? In fact, given his immigration status, I am not even sure if he could legally remain in the country beyond the normal grace period that is extended to visitors. And there would be restrictions too on his ability to work or get a paid job.
It seems to me that, despite H&M's talk about colonialism and dealing with its legacy, it was Harry who was confusing the Commonwealth with the old British Empire and showing a colonial mentality with respect to Canada, New Zealand and South Africa, which is out of touch with their current status as sovereign, independent countries.
One of the alleged reasons they quickly rushed to LA before the border closed was that their visa was up and couldn't be extended because neither of them were working or citizens and hadn't planned for that possibility.
You're right it seems like quite a colonial and unrealistic attitude to think "oh, we'll go to wherever, be "official royals" there whilst doing our own thing and the taxpayers will even pay for our security." That and believing your own hype.
They showed they didn't understand the Commonwealth at all with their previous comments, especially the fact that it's an entirely voluntary organisation which countries who were never even part of the British Empire want to join.