Regarding the wedding options of the Habsburgs, some things could be different.
Anna of Bohemia & Hungary was to marry a Habsburg archduke, but Maximilian was clever enough not to specifically mention, which one in the treaty.
Furthermore the Habsburgs actually favored a French or an English princess as a spouse for Charles V. However when that basically took too long, they started to look for alternatives. Before Mary Tudor eventually married Louis XII of France, she was also considered as a marriage candidate for Charles V. After that wedding cardinal Wolsey did offer the young Mary Tudor (daughter of Henry VIII), but she was much too young for Charles, who really needed a heir.
Still with Charles V ruling Castille and Aragon, and with no French or English princess old enough to marry, a Portuguese princess like IOTL and archduke Ferdinand marrying princess Anna like IOTL seems likely.
Changing that, like Charles marrying Anna instead, would require that the Habsburgs never inherit 'Spain' (or somehow Ferdinand inherits the Spanish kingdoms, which is rather unlikely). OTOH such a PoD will most likely be that early, that more things will change.