Oh, thats quite not possible, currently reflection system does not support TMaps, only TArrays is supported from all container types. You might try to do something with this, but not sure if this will work:
you definitly won’t be able to use TMaps in blueprints or else you make nodes to operate specific TMap in C++
TMap support for reflection system and bluepruints overall was requested few times and it’s considered to be implemented in future