On the XIII until the XVII centuries AD the Kingdom of Denmark controlled parts of the baltic, as it can be check on this map. Since Denmark became a very peacefull country after the war with Prussia I believe that a 19th century PoD is more realistic for the situation. Let's say that after the Holstein war the Danes keep their highly nationalistic policies, and when Wilhelm II comes to power and refuses to sign the insurance treaty with Russia, Denmark begins to approach Germany, to the poin that they join the central powers somewhere in 1915/16 (maybe after the fall of Serbia). Can they hope to Get Estonia, and maybe Latvia on Brest Litovsky too?