I'm not sure that the Baltic States would be at their pre-war boarders as three nations, for several reasons.
The Germans had serious "Germanization" plans for the "Ostland Reichkommissariat" which included seriously encouraging German settlement and, if
the Wikipedia article is to be believed, removal of "undesirables" to Belarus.
Seeing as that the German settlers will be removed by force and that the remaining pre-war population, or at least that which was not considered "German" enough, has been at best forced to move into Belarus and probably exterminated to a similar degree as the Poles ITTL, I don't find it likely that there would be sufficent population to reform all three nations. As for the pre-war population that was allowed to stay because they were considered "Aryan" by the Gestapo, well, see Austria. An entire generation that considered themselves as Aryan as someone from Berlin.
In light of this, I see one of three options occuring post-war:
1. (Most likely) The Baltic States, due to the little remaining pre-war ethnic populations, are not reformed as 3 seperate nations but are combined into a United Baltic Republic in the hopes that, being united, they stand a chance to form a viable, if not prosperous, nation.
2. (Possible) The Baltic States are not reformed as three nations, or one, but are absorbed in whole or in part by one of the new East European nations.
One scenaio I thought of was Belarus gets Latvia and Lithuania (access to the sea, and, according to Wiki, most of the remaining Ethnic populations of those states would be moved there. With Estonia possibly going to either Belarus or more likely (IMO) Tsarist Russia.
3. (Least likely) Due to extremly high amounts of German settlement and ethnic cleansing of pre-war population the former Ostland is basically treated like Austria. It is broken into 3 German "successor" simply to prevent a large German state from existing there. This is only a possibility if the the original Ethnic population has been eradicated too much for option one or two.