I didn't quite understand what you meant by the Crown of Castile defeating the Trastamaras. Did you mean that Pedro I wins the 1366-69 Castilian Civil War?
If so, I'm afraid I don't have an exciting answer. From Enrique II to Juana all the Trastamaras were very different people and they'll all be butterflied away and it's hard to predict the character of who'd reign in their place.
If the Barcelona dynasty still dies out, a Castilian prince is still a very good candidate to take the Crown of Aragon.
Butterflies will hardly allow the coincidence of precisely a Castile-Aragon-Burgundy-Habsburg union of crowns taking place. But some Iberian and European consolidation with come along, each variation with its own butterfly effect waves.