You could absolutely stretch/fill the display. There was an option in settings to adjust the horizontal and vertical so that you could stretch the image to fit your screen. I have had to do this every year for the past few years.
PS4 version does not require it.
As for 1080p. I know there were a couple of editions that let you output in 1080p if you adjusted the PS3's resolution settings. I think you had to make 1080p the ONLY option and then when you loaded up the game it would output at that. Framerate would take a hit though.
Image quality is definitely decreased though on 1080p. Doesn't make sense, but they mean it when they say play it at 720p. I have no idea why this is the case, but I've compared screenshots side-by-side and the visuals are not improved on 1080p at all.
They really need to do some work on the front end of the game when you first get into the game. Hiding stuff in the menus is why sports games get a bad wrap from more casual fans.
- autoplay intro sequence ONCE, then disable it once a save is created
- do the "adjust size to fit display" screen on first boot
- A proper tutorial that goes through the different hitting and pitching control options so new players know there are many options to pick from.