"מנהיגי שלש ארצות יצ"ו" In his introduction, Kli Yakar mentions leaders of three lands who "dwell first in the Kingdom of Heaven". Is he mentioning three actual people who helped him print his sefer? Or something else?
The three lands being referred to at that time (17th century) were Poland, Lithuania and Royal Prussia. These were the territories occupied by the western Slavic peoples.
This introduction was written pre-Chilmienicki Poland and was a state called the Polish-Lithuanian Commonwealth which was formed through the Treaty of Lublin. It was considered a time of relative tolerance for the Jews. It was ruled by an elected Monarch together with a Senate and Parliament.
From what the Kli Yakar writes in his introduction at the end, he received some form of governmental contribution (economic assistance) to assist in the publication of his commentary which he refers to in the plural (from their pockets, etc.). But in terms of the history of the Commonwealth at that time, it was possible he was referring to King Augustus II the Strong who was known as being a personal patron of the arts.