Anyone who has already visited Cadiz knows that nobody can hold Cadiz against the continent. Cadiz is not a rock like Gibraltar.
If you want some crazy turn of events with Spain, have marriages between 1 or 2 Plantagenet king of France (instead of his younger sons like John of Gaunt or Edmund of Langley) and a woman kawful heir of the crown of Castile. The sooner the better.
It should then not be too difficult to have the Plantagenet king extend his rule to Aragon and Portugal.
Concerning France, you just can't hold Britanny and Calais in the age of artillery. That's precisely why Calais fell in the mid 16th century. Land powers had too strong firepower for England continuing holding Calais.
The only way to have a solid UK of England of France is, at the latest, to have Edward III be chosen as heir by his grandfather Philip IV of France.
Have Philip IV live 15/17 years longer until 1329/1331. He has no living son left (they are dead in 1316, 1322 and 1328) and his 3 sons only left daughters.
Then, have Philip IV and his daughter Isabelle agree on the fact that Edward is going to be king of France and England.
This would form a "UK" for the small minority who would still speak english a few centuries later. And the wide majority would rather call it RU for "Royaume-Uni".
All the principalities that were to be known as the burgundian low countries will of course be under the domination of the super Plantagenet king.
Starting from this point, you can have the UK of France-England-Castile-Portugal-Aragon conquer Rhineland and whatever it wants in Italy.
You can then have it conquer and colonize all Americas and prevent any other kingdom founding colonies on the north and south american coasts.
Is this enough ?
The only point that may disappoint you is the language. If the king of England rules other kingdoms with a much larger populations (the kingdom of France in its medieval borders was 5 times as populated as England), then England in itself will be satellized by the much bigger kingdom of the dynasty.