And it got me thinking how could we end up with a complete integration of the three bolded countries into Germanic speaking Europe and what would the effect be?
I don't think it's going to be that hard, Latvia is the easies you just need a few German free peasants in the countryside, the cities was already German. Finland is also relative easy if Sweden had keeped it to 1900 at least, I think we would have a majority Swedish-speaking Finland, Estonia is hard it shifted hand more often than the others, the Germanic minority was split between a Swedish population at the coast and on islands and a German urban population.
The best solution could be a later black death, it would mean a continued emigration from Germany and Scandinavia to these East Baltic countries, at least until the plague does come.