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Say Maximilian II compels Rudolph II to marry early to Maria Eleonore of Cleves and suggest that Isabella Clara Eugenia wed Ernest of Austria instead with a set up similar to her OTL marriage to Albrecht.
Now I know Philip II of Spain only made those arrangements because Rudolph didn't honour the marriage to Isabella Clara.
I'm proposing the Maximilian II is the one who suggests such a proposal and to sweeten the pot and make up for the cancelled engagement offer to elevate Isabella Clara to Grand duchess of Burgundy/ more specifically elevate Franche-Comte to a grand duchy (the claims/pretense was already there, Philipp the Good & Charles the Bold held such titles)
Possibly add the demesne as well with territory in Further Austria (Alsace-parts) since it would be expected for it to fall back to the senior imperial line as Ferdinand II of Futher Austria had a morganatic marriage.