I tried the same sequence, with the same airplane on default CYYZ, and when it came to deboarding, the two baggage wagons came loaded with ULDs after a minute or so, and they boarded the airplane normally, so that I could start Pushback.
Some things to check:
- If you made or downloaded a custom configuration for the 777, you don't need it, because it's an internally supported airplane. Use the "Reset" button in the airplane configuration editor to restore to the config that comes with GSX.
- If you downloaded a GSX config file and placed it in the FSX\Simobjects\Airplane folder of the 777, you must remove it manually, because the "Reset" option won't remove it (that folder it's supposed to be used by 3rd party developers that supply a pre-made GSX config, so the Reset won't touch it)
- If still doesn't work, try to remove all your GSX preference, by removing the following folder:
%APPDATA%\Virtuali
Then REINSTALL GSX, using the latest full installer. Note that, this will remove all your custom configuration files for both airplanes and airports, so you might want to move the folder to another place, instead of just removing it.