Thanks Plamen,
1. I got the Hyper-V virtual machine inventory list using the below API.
_converterService.converterQueryHyperVInventory(..,...)
2. Then i set the source VM's GUID in the ConverterComputerSpecHyperVComputerLocation.vmGUID field.
Automatic migration of VM from Hyper-v to vSphere is successfull now.