I've tried to find info about the usb connector of canon dslr cameras, but found nothing.
The question of host/device I know and if the camera act only as a device, the gps can be a host with the appropriate hardware.
The idea is to build a dedicated device for this task.
Beyond that, I don't know if every time a photo is taken, magic lantern can access this usb port to get the geographic coordinates and insert them in the exif information.
If you have any further info, please point me.
Regards.