John Casimir, then "jobless" younger brother of Polish king, was offered that office by his Habsburg cousin and was on the way to Spain in 1638, but was captured and imprisoned in France for almost 2 years, before he was released in February 1640 and allowed to return home.
So what if he avoided arrest on French soil and reached his destination? Portuguese revolt against Philip IV started just 2 years later, I doubt John Casimir is going to prevent it, if that was ever possible. If he avoids troubles in France he's not going to met his future wife Marie Louise Gonzaga there, OTOH he may be married into Portuguese or Spanish aristocracy. After Portuguese revolt he's going to be jobless again, propably he departs to Spain.
And how is his Iberian adventure going to impact things in PLC after his older brother dies? Certainly election of 1648 and fate of Marie Louise is not going to look like IOTL.
@Zygmunt Stary
So what if he avoided arrest on French soil and reached his destination? Portuguese revolt against Philip IV started just 2 years later, I doubt John Casimir is going to prevent it, if that was ever possible. If he avoids troubles in France he's not going to met his future wife Marie Louise Gonzaga there, OTOH he may be married into Portuguese or Spanish aristocracy. After Portuguese revolt he's going to be jobless again, propably he departs to Spain.
And how is his Iberian adventure going to impact things in PLC after his older brother dies? Certainly election of 1648 and fate of Marie Louise is not going to look like IOTL.
@Zygmunt Stary