Let Karl XI Gustav annex Denmark 1660 and the Sea Powers for some reason accept it (halving the Sound toll, perhaps?).
From there, campaign to tie the Swedish posessions in northern Germany together - Schweswig, Holstein and Gottorp to Bremen, Lauenburg and Mecklenburg-Schwerin to Wismar and Vorpommern.
With Norway, Iceland and Greenland added with the Danish annexation this is a lagre realm.
Adding Courland in a war against Poland-Lithuania, Far Karelia and Kola in a war against Russia and then some colonisation and you have a large realm.