The Barren Grounds by David A. Robertson

Narnia meets traditional Indigenous stories of the sky and constellations in an epic middle grade fantasy series from award-winning author David Robertson.
Morgan and Eli, two Indigenous children forced away from their families and communities, are brought together in a foster home in Winnipeg, Manitoba. They each feel disconnected, from their culture and each other, and struggle to fit in at school and at their new home - until they find a secret place, walled off in an unfinished attic bedroom. A portal opens to another reality, Askí, bringing them onto frozen, barren grounds, where they meet Ochek (Fisher). The only hunter supporting his starving community, Misewa, Ochek welcomes the human children, teaching them traditional ways to survive. But as the need for food becomes desperate, they embark on a dangerous mission. Accompanied by Arik, a sassy Squirrel they catch stealing from the trapline, they try to save Misewa before the icy grip of winter freezes everything - including them.