The Emperor Matthias married rather late, to a cousin Anna of the Tyrolean Habsburg line. They had no children precipitating a succession struggle in Bohemia that led to the 30 Years War. I'm wondering if Matthias married differently and had a son. His wife would probably have a role in any regency as the child would only be about 8+/- years old. Anna was apparently considered as a bride for Sigismund III or Poland so she could simply marry him or just die young. Looking around there weren't many alternatives available.
Magdalena of Bavaria 1587-1628
Matthias courted her but her brother refused to countenance the match. She is also apparently was in love with his cousin Leopold of Inner Austria. She'd likely align with the Catholic League which could be problematic.
Constance of Inner Austria 1588—1631
OTL Queen of Poland as second wife of Sigismund III, her late sister's widower. Probably more likely if Sigismund marries Anna of Tyrol. It could be a way to heal rifts in the family that emerged during Rudolfs reign. She was, like her brother Ferdinand II devoutly Catholic so that could create friction with the Bohemian and Hungarian Estates. She'd probably agree to her brother being elected Emperor on Matthias' death but she certainly support her own son over her nephew in the next election. She supported her son John over her step son Wladyslaw OTL.
Eleonora de'Medici 1591-1617
She was put forward as a wife for the widowed Philip III OTL but he refused. She later died from smallpox so there's every reason to believe she could have lived longer. Her family was looking for a Habsburg match after falling out over her father's marriage to Christina of Lorraine, who as a descendent of the Valois line was considered pro-French. His niece's marriage to Henry IV didn't help that perception. She would be interesting as maybe less rigidly or dogmatically Catholic. She'd also be a first cousin to Marie de Medicis so her son would be a second cousin to Louis XIII.
So I'm wondering if there are any other more logical choices and how each would handle a Regency for Upper, Lower and Further Austria, potentially involving Matthias' brother Albert and/or his cousins in Inner Austria. Bohemia and Hungary are nominally elected, not sure they'd elect a minor, their estates would surely want great concessions. Likewise how the Imperial Election would play out. Eleonora would have the fewest allies so she could either play them all shrewdly to her sons advantage or find herself isolated. Magdalena might rely to much on her brother creating a rift with the Inner Austrian Habsburgs. Constance with her strong Catholicism may face the same problems her brother faced in Bohemia OTL.
Magdalena of Bavaria 1587-1628
Matthias courted her but her brother refused to countenance the match. She is also apparently was in love with his cousin Leopold of Inner Austria. She'd likely align with the Catholic League which could be problematic.
Constance of Inner Austria 1588—1631
OTL Queen of Poland as second wife of Sigismund III, her late sister's widower. Probably more likely if Sigismund marries Anna of Tyrol. It could be a way to heal rifts in the family that emerged during Rudolfs reign. She was, like her brother Ferdinand II devoutly Catholic so that could create friction with the Bohemian and Hungarian Estates. She'd probably agree to her brother being elected Emperor on Matthias' death but she certainly support her own son over her nephew in the next election. She supported her son John over her step son Wladyslaw OTL.
Eleonora de'Medici 1591-1617
She was put forward as a wife for the widowed Philip III OTL but he refused. She later died from smallpox so there's every reason to believe she could have lived longer. Her family was looking for a Habsburg match after falling out over her father's marriage to Christina of Lorraine, who as a descendent of the Valois line was considered pro-French. His niece's marriage to Henry IV didn't help that perception. She would be interesting as maybe less rigidly or dogmatically Catholic. She'd also be a first cousin to Marie de Medicis so her son would be a second cousin to Louis XIII.
So I'm wondering if there are any other more logical choices and how each would handle a Regency for Upper, Lower and Further Austria, potentially involving Matthias' brother Albert and/or his cousins in Inner Austria. Bohemia and Hungary are nominally elected, not sure they'd elect a minor, their estates would surely want great concessions. Likewise how the Imperial Election would play out. Eleonora would have the fewest allies so she could either play them all shrewdly to her sons advantage or find herself isolated. Magdalena might rely to much on her brother creating a rift with the Inner Austrian Habsburgs. Constance with her strong Catholicism may face the same problems her brother faced in Bohemia OTL.