What if the US just took everything it could, leaving only mainland Spain under the control of Madrid? All of these become American colonies:
-Cuba
-Puerto Rico
-Philippines
-all of Micronesia
-Canary Islands
-Western Sahara
-Equitorial Guinea
-Balearic Islands (an American Malta)
From that list, I could see Micronesia, the Canaries, and the Balearic Islands becoming states #51-53 because they are all so strategically placed for the navy. Cuba would have the same difficulty Puerto Rico would have at becoming a state and may become independent, as would the Philippines and the African colonies in due time.
WWII is easier because Japan will not have Micronesia from the start and to fight in North Africa we would just have to land in the American Sahara rather than fight in French Morocco.