I've been trying to set up Baldur's Gate 2 (original) all night. After installing the widescreen mod, the game indeed ran full screen. Problem is, the native resolution of my laptop screen is 1920x1080, and at that resolution everything is just too small. So I set the resolution to 1280x720 in the widescreen mod, and changed the resolution of my screen to 1280x720. But when I start BG2, screen resolution changes back to 1920x1080 and all I have achieved is that I'm now playing in a "window" surrounded by black.

My laptop is running Windows 10, and is equiped with Intel HD Graphics 4600 & NVidia GeForce GT 750M GPUs. Apparently the system using "Optimus" technology (just learnt about that today) to switch between the GPUs. Because of that I can only change 3D settings in the NVidia control panel, not display settings. I suspect that is where the problem lies; when I start the game the system automatically switches to the GeForce GPU which resets the resolution.

I've gone through a whole list of topics on this forum about similar issues with BG2, but haven't found a solution that works for me there. I hope someone out there can help.

I think you should keep your screen at native resolution, without lowering it.
If you want to play at lower resolutions and you also want the game to fill your screen, you have to enable scaling: both Intel's and nVIDIA's drivers can scale your current resolution to full screen.

If the game runs using the nVIDIA GPU...
Open the nVIDIA Control Panel and select "Adjust Desktop Size and Position" in the "Display" menu: there you can set the preferred scaling mode.

If the game runs using the Intel GPU...
Open the Intel HD Graphics Control Panel and navigate to the "Display" section to select the desired scaling option.

Scaling the resolution will make your game look worse but lowering your resolution will do as well.

Thanks for the reply. As indicated, there is no "Display" menu in my nVIDIA control panel. An extensive internet search has revealed that this isn't a bug, it's a "feature" of the Optimus technology, and there is no way to make this menu appear.

The comment about the Intel HD Graphics Control Panel was useful though, I hadn't considered looking at that yet. While counterintuitive, what ultimately solved the problem was to set the scaling in the Intel control panel to "scale to full screen", even though the game has been set to use the nVIDIA GPU in the nVIDIA control panel. I guess this setting reads across somehow.

I'm not sure, but nVIDA driver probably uses the same display settings of the Intel one: that could explain why you don't see any "Display" section in the nVIDIA Control Panel. This could be the Otimus' feature you are talking of and somehow makes sense because it's not logical to have different display settings for the two GPUs.

Same problem as yours! I cannot find any solution to solve it, however.
The Intel Graphics card controller is not a factory component on Surface pro. And if I try to install it by myself, it might cause some unknown problem with the official updates.
That's too bad...(