"Of course they need to nurture the relationship with Canada. However ‘thank you for being nice to us, the British public have vilified us and we’re so grateful you are kind’ is the not the right note to strike. "
I disagree on this actually because I think the key point here is that this bit of work and PR isn't aimed at us in the UK. It's aimed at Canadians. They want Canadians to feel warm and fuzzy to the royal family in general, and Meghan and Harry in particular. They want Canada to feel a close tie to the UK. They don't want to risk Canada ever considering exiting the Commonwealth or taking it less seriously and they want all Canadians and people in power to continue to see the UK as a close ally.
And actually I think the fact that in the UK we can't see the importance of strong diplomatic and emotional ties to countries like Canada and the way in which the royal family help to nurture these as quite worrying in a world in which the US president is a hair trigger away from causing all out global war and traditional allies are confused and erratic.