Sample ABAP code to launch a SAPGUI transaction from WebDynpro. This is similar to how its done with FPM (if_fpm_navigate_to). See the example GIST on that.

web_dynpro_launch_tcode.abap

ls_transaction-tcode = 'BSSP_BOR_OBJECT'.
ls_transaction-gui_type = 'WIN_GUI'.
ls_transaction-system_alias = 'SAP_LocalSystem'.
ls_lpd_tx_para-key = 'SWO_TYPEID'. "'OBJKEY'.
ls_lpd_tx_para-value = ld_string+6(70).
INSERT ls_lpd_tx_para INTO TABLE ls_transaction-parameter.
ls_lpd_tx_para-key = 'OJ_NAME'. "'OBJTYPE'.
ls_lpd_tx_para-value = ld_string+76.
INSERT ls_lpd_tx_para INTO TABLE ls_transaction-parameter.
ls_lpd_tx_para-key = 'RFCDEST'.
ls_lpd_tx_para-value = ms_object_info-rfcdest.
INSERT ls_lpd_tx_para INTO TABLE ls_transaction-parameter.
ls_lpd_param-navigation_mode = 'EXT_HEAD'.
ls_lpd_param-parameter_forwarding = 'P'.
*          ls_lpd_param-batch_input_program =
*            'BSSP_BOR_OBJECT_DISPLAY'.
*          ls_lpd_param-batch_input_dynnr = '1000'.
*          ls_lpd_param-batch_input_ok_code = 'ONLI'.

ls_lpd_param-skip_init_screen_if_possible = 'X'.

CREATE OBJECT lo_navigate TYPE cl_apb_launchpad_launch_api
  EXPORTING
    ir_wd_component = io_component.
    
lo_navigate->launch_transaction(
  EXPORTING
    is_transaction_fields    = ls_transaction
    is_additional_parameters = ls_lpd_param
  IMPORTING
    et_message = lt_message_ ).
    
LOOP AT lt_message_ INTO ls_message_.
  mo_msg_manager->report_t100_message(
    msgid     = ls_message_-id
    msgno     = ls_message_-number
    msgty     = ls_message_-type
    p1        = ls_message_-message_v1
    p2        = ls_message_-message_v2
    p3        = ls_message_-message_v3
    p4        = ls_message_-message_v4 ).
ENDLOOP.