For VLC I don't know, but with MPC-HC you can use madVR [0]. My preferred setup is mpv [1] with a few shaders [2] such as FSRCNNX [3] and Krig Bilateral.
Most televisions only render at one resolution; they don't have the ability to dynamically resize the "window" of the player. I've always just assumed upscaling on the TV is just the same as fullscreening VLC on a large monitor.
Most televisions nowadays have built-in upscaling so you'd think something would exist for the desktop PC market.