There are probably many ways you could spin it, but my primary thought is that Montaigne would be Envy.  It seems like many in the noble class are obsessed with one-upping each other in court.

They are all Vodacce.

No, but true. Pride is as much a danger in a Castillian as it is Avalon. Pride is what drives the Inquisition as much as fear in that they believe only they are correct. Same argument goes for Wrath. But the issue is the placement of Sloth. It doesn't fit any of the nations. Certainly not the agrarian Ussura. It has it's best hooks in Montaigne nobility and they are far from a textbook example. I guess the point I am making is that every nation could be an example of any of the sins. Sarmatia could be sloth due to the stagnation of politics, Castille for the siesta, Inismore for the pubs, Vesten for the guild system where the master earns on the efforts of the apprentice. So build it to what you want to focus upon.

Ussura is tough. The wrath of grandmother winter, is it lust in the form of love of the land and the embracing of joy of life? Is it envy of the advancements of other lands or pride in doing things the old way? I think Despair stays in Eisen.