Anonymous: Is it possible for nations to have children? (Like with Ancient Greece and Greece, Ancient Egypt and Egypt, etc.)
We simply do not know!
While Ancient Greece and Ancient Egypt are often referred to with the title of mother, this might imply their status as mother figures - not necessarily biological parents.
When Egypt and Greece came in to this world, they had two fully-grown nations to look after them - unlike some other nations, who did not have these sort of parental figures. Ancient Greece and Ancient Egypt may have, historically speaking, ‘born’ the nations of Egypt and Greece into the modern world, whether or not there was a conventional biological connection.
A joke during the 2007 April Fool’s event implies that male nations can have children; however, as the initial comment comes from an outside source, and is in a humorous context, the idea that nations can have children may still be taken with a grain of salt.
At the very least, the idea that nations can produce new nations through birth is shaky in canon. Ultimately, the direct origin of nations is a topic only touched upon vaguely.
In any case, whether or not they gave birth to Egypt and Greece in the standard sense, nations can have children - in the sense that they can be parents! If you take parenthood to simply mean the act of parenting, then Ancient Egypt and Ancient Greece were undoubtedly wonderful mothers to their young protegee.
Anonymous: Are there any actual canon interactions between Prussia and Canada?
There is a case of off-screen interaction between Prussia and Canada!
During the 2009 April Fool’s Oresama no Blog event, Prussia makes a post to his blog regarding the fact that Canada gave him a free bottle of maple syrup. Prussia went on to find a new-found love for pancakes.
Anonymous: Top 3 pairings in Hetalia most likely to be canon?
As always, defining a canon pairing is tricky - and defining a top three is even more difficult!
However, in terms of canon, a few combinations stand out.
In no particular order:
Austria and his marriages are unique. Austria has been married a few times, both to Spain and to Hungary. These marriages were representative of the House of Hapsburg and the Austro-Hungarian Empire, respectively. Austria has and continues to have a noteworthy closeness to Hungary, and some consider the pairing canon due to their history as a married couple.
Holy Roman Empire and Chibitalia shared a kiss.
Greece and Japan appear to have engaged in some form of sexual activity.
If intimate relations, kissing, and marriage are a fair basis to analyze the canonical nature of pairings, than the three pairings above offer various factors above and beyond Hetalia’s usual pairing-reticent content.