The most Northern power in Medieival America is Quebec. starting at the end of the Gulf of St. Lawrence, although it's never been a part of the United States, the fractured feudal states means that it could never quite sit out on politics. The rest of America will tell stories of stories of axe-wielding Barbarians. Although darker times have made the nation fearsome, it's also a rich warrior culture. It has also in recent times become wealthy due to the fur trade, and deposits of gold.
The Quebecois French has largely been kept intact. This comes from a relatively small and consolidated populace along the St. Lawrence. The language has always been a distinctive part when it was a province of greater Canada, and in the medieval age, the Quebecois look at it something that marks themselves as a race. Therefore, any major breaks from the tongue have been considered as good as heresy. A french language makes up the court, as well as the Catholic Church. The Non-Denominational Church was looked at as an American, Anglo institution, and was thus never embraced in these parts. In fact, the Quebecois are the only sizable population not to practice Non-Denomination east of the Mississippi.
Because the land itself is so cold, and because their uniqueness has given it a sense of superiority, Quebec has long waged expansionist wars on the continent. New England has largely had little to fear from the kingdom. The rugged terrain of the Appalachians, particularly the Green and White mountains, have kept Quebec's knights at bay. Therefore, most attacks have been at the westward countries. Every couple of centuries, attempts will be made to conquor New York, for its warmer and fertile fields and vineyards. Access to the Hudson River is also a benefit, as the Hudson is a pivotal gateway between east and west. Quebec will also try to absorb its Canadian neighbors, feeling the lands of Canada were always rightfully Acadian. Invasions peter out or hit a brick wall at Toronto, and even though Quebec's empire is at a vestigial point, it did have the effect of breaking up the Province of Ontario, and eastern Canada is now a spectrum between Anglo and Franco cultures.