Maybe anti Spanish sentiment in the United States become stronger. They were in otl not happy with a Spanish Cuba, they would even be less happy with any territory that made up the US in reality under Spanish control after 1830, especially because the threat to the American security would be worse.
Perhaps, an earlier Spanish American War over Florida and Cuba or US interventions in Cuban [and Floridan] insurrections. If the war still happens in 1898, the US would invade the peninsula. Of course, Florida would be a higher priority than Cuba because it is closer, and more importantly, on the mainland. But, it might be enough for the Spanish to win because they can ship more reinforcements to Cuba and the US would need to be fighting in Florida for months and blockading it before taking Cuba, presuming the Spaniards utilize their navy properly [almost certainly expanded compared to otl] and send adequate troops and supplies to Cuba [Florida would soon be lost anyway and Puerto Rico is not so important]. The US might cancel its invasion of Spanish Philippines and Guam to gain more troops and ships. This might result in the colonies gaining independence [for the Philippines] or sold to other powers [especially Germany].
Maybe Florida would try to declare independence, but no Florida Cuba Union. Or, if this happens, expect the Cuba Missle Crisis to escalarate into a full scale war as the US might invade Florida and risk war with Cuba. [Assuming butterflies don't create many problems].