The reason newfoundland is dense is because it was the perfect location for Ireland, thats all. I re-rearranged from the previous version and it was quite challenging, so re-re-rearranging it even more is pretty daunting
That's what I figured, and what I would do in your situation. However (and perhaps I'm just a bit biased here

), I do think California should have comparable province density compared to the East Coast, rather than Montana. De Jure Ruthenia has ~23 or so provinces on your map, around the same number as in Florida. If those were crammed into California, the density would be just enough, though it would actually still be less than Florida and most of the East.
Depending on how much effort you're willing to put into it, within the region, there should be much greater density around the Bay Area and the Central Valley. LA may be the largest city west of the Mississippi today, but in a pre-modern society, the fertile agricultural land and traversable rivers of the Valley would support far higher population density in the north than in the south.