Three Day Road - Joseph Boyden
Set in (and before) 1919 in France and Belgium, and Northern Ontario - and the sex, my god, the sex, it comes out of nowhere, people throw off their clothes like didn't have any - but more often it's the story of two Cree who become snipers in WWI.
Injuns and the Somme are by now familiar stories, of course, but I'm finding this one fresh and compelling.