External Monitor GPU Question
That seems like something that would be better asked of Lenovo, not Arena Net or Guild Wars 2. It would likely be a BIOS setting or configurable through a Lenovo utility or Windows driver configuration, if it’s something that can changed by the user.
I would think that GW2 would be “at the mercy” of whatever display driver that DirectX/Windows chose to connect it to when the game asked DirectX/Windows what kind of hardware it was running on. I don’t think that GW2 is able to tell DirectX/Windows what driver to use for a particular display device.