I understand that you are trying to connect bus ports for an exported FMU with simscape model.
As you may know, FMI2.0 and FMI1.0 standards only accept scalar as ports. To comply with FMI standards, Simulink needs to expand Bus signal and array signals, etc into scalar signals. For Buses, Simulink uses the following strategy:
bus1-subbus1-signal1 -> bus1.subbus1.signal1
-signal2 -> bus1.subbus1.signal2
-signal3 -> bus1.signal3
in 2020a+, FMU import block should automatically group scalar signals of a Simulink exported FMU back to Buses, which means you can to directly connect the buses to FMU Import block. For other use cases, the FMU users need to manually connect the scalar signals. You should be able to use a bus selector block to achieve so.