I would guess that Blunflo is the best capital for Jamtland and Harjedalen. It's about 20 km south-east of current Östersund (founded 1745 so Östersund is outside our time-period). It seems to be the best choise. Otherwise you could choose Sveg if it makes for a better map.

Some areas in northen Sweden could be made impassable, but you should be able to tavel from Norway to Sweden at some places up there. I should take time to do so though (= thickest passable forest).