Eirik II, King of Norway married first a Scots king's daughter (Margaret of Scotland) and then a Scots king's sister (Isabel de Bruce), but had no sons, only daughters to show for it - a daughter from each marriage.
But what if his daughter from his first marriage - the famed Margaret, Maid of Norway - had been born male instead? Would a personal union between Scotland and Norway be on the cards? Or would Eirik's younger brother, Håkon (OTL Håkon V) take the throne of Norway while his nephew is in Scotland?