Actually, this is amazingly simple. It takes just three divergences:
1) Henry VI of England dies early, avoiding the Wars of the Roses*.
2) Henry VI's uncle Humphrey doesn't leave descendants, either.
3) King Erik III/VII/XIII of Norway/Denmark/Sweden has a son who continues his line.
Why is this?
Let's look at the descendants of Henry IV of England.
I. Henry V of England
---A. Henry VI of England
------1. Edward, Prince of Wales (rid of whom we're getting)
II. Thomas, Duke of Clarence (no legitimate children, d. 1421)
III. John, Duke of Bedford (no children, d. 1435)
IV. Humphrey, Duke of Gloucester
---A. Arthur (no children, d. 1447)
---B. Antigone (had children--but we're getting rid of this line, too)
V. Blanche
---A. Rupert of the Palatinate (no children, d. 1426)
VI. Philippa (who married Eric)
---A. That new line of sons, by (3)
So, without the deposition of the Lancasters, the heirs to England are also the rulers of the Kalmar Union.
And the ruling house of the Kalmar Union is that of Pomerania, i.e. the house of Griffins--originating among the Slavs!
*At least one hopes so for the purposes of this mini-TL.