You need a supported card and I think it would work best with the same aspect ratio. 1400 x 900 is closer to 16:10(1920 x 1200) than it is to 16:9(1920 x 1080).
You can try to add a custom resolution like 1920 x 1234(sounds odd, but 1400 X 900 scaled to a 1080 x XXXX would be a factor of 1.371) to see if it works. It would not be a huge upscale/downscale either.