It might be possible to ask (or hack) Starcraft to render the game at a massive resolution, large enough to show the whole map onscreen. If your projector has a HDMI input then you can just treat that as your monitor. But then if the projector only accepts an HD resolution image then you'd need to modify Starcraft to downscale the image, which is probably a non-starter. And it might even be too slow to render the whole at a normal frame rate anyway. (It's only 2D, but wasn't necessarily optimised to take advantage of modern hardware.)

This isn't too hard in the remake, and can be done with the editor. But lod comes into play and things stop rendering that far zoomed out...

Just play supreme Commander instead, i guess.