I knew, of course, of the Prince of Hesse-Kassel candidature, but it appears he was not a 1st choice.
King Gustav V hoped a Bernadotte prince might be selected but the finns rejected on the grounds of lack of swedish support on a civil war in the beginning of 1918.
A war that caused a high toll of deaths of more than 37.000 (acc.Wikipedia).
After the swedish candidate, came Grand Duke Adolf Friederich of Mecklenburg-Schwerin who had prooved to be a reasonable governor of Togo in Africa.
Next came Prince Oskar, a younger son of Kaiser Wilhelm, who refused the offer, thinking that an eventual dethronment of his son could harm the prestige of the Hohenzollerns.
In turn, he admitted his cousin Friederich candidature.
Only after this candidature came Friederich of Hesse who was the most serious candidate, got a majority of votes in the finnish parliament but was refused by France and UK who deemed someone so close to the kaiser would influence Finland to the german influence and threatened to break relations with Finland.