There is a long-distance transmission line in California that is used a bit like this, allowing the use of power from the North in the South in summer when peak

There is a long-distance transmission line in California that is used a bit like this, allowing the use of power from the North in the South in summer when peak demand is there, see https://en.wikipedia.org/wiki/Pacific_DC_Intertie https://en.wikipedia.org/wiki/Pacific_DC_Intertie The Pacific DC Intertie is not nearly as long as a connection between CA and FL would be. In that scenario, transmission losses would be quite significant. The cost of building and maintaining the line would also be quite high.