Hi Ravi,
I’m not sure exactly where you see esc_status_sub_cb being called, at least from the latest PX4 drivers/uavcan/actuators/esc.cpp file. The callback function gets setup in the init() function of UavcanEscController class and then the uORB topic gets copied in uavcan_main.cpp.
If I understand correctly, the uavcanesc driver is the driver for setting up an actual ESC device. Are you trying to set up this device as an ESC or are you trying to connect an ESC to it?
If you are trying to interface with another ESC, you need to make sure the UAVCAN ESC is publishing the status message.
Jon