Hello, and welcome to GD.net!
So as it is now, what you are shooting for may be a bit out of reach. I can't speak to your skill level, but from what I read, I'd say you're just starting out?
We're using Yo-yo Games' Game Maker program. I know this is usually used to create casual games, but I'm confident that it will allow us to implement all the gameplay elements we need for R. I'm less certain about how well we can actually produce a product that can be played on different systems. Ideally, I'd like to see this game on both PC and PS3, but resolution problems are currently a cause for concern.
GameMaker isn't a bad tool. It's fairly basic and clunky, but you can rapidly prototype and test your game. I used it for roughly 4-5 years, and I very much enjoyed it. However, it is a restrictive tool. You won't get amazing performance, but it will be good. That being said, I don't believe PS3 development is part of GameMaker, as with most consoles. This, I'd say is what you should be concerned about least, especially because porting to any console is a huge investment. This is because you need a development kit, or at the very least a $1200 debug PS3 to actually run and test your game on the platform before they accept it and put it onto the network (which they also have a certification process before any of that as well). You can read more about it here: http://www.gamasutra.com/php-bin/news_index.php?story=17707
PC is always a viable and easy option for publishing, so for now I would recommend that you stick to that.
Right now we're coding the game in 1280x720. But what happens when this is played on different screens? Our graphics are all pixel-by-pixel drawn sprites; expanding them by anything other than 2x is going to ( I think? ) look horrible and distorted. I'd rather not expand the view distance on the windows, but would that be necessary? What happens if someone plays this on a standard-definition television? I keep thinking about these questions and having no answers makes me realize just how little I know about what I'm getting into.
So what you're experiencing is a screen resizing issue, and in GameMaker, there's not all too much to be done with that. If you go into the global game options, there's an option along the lines of "interpolate colors between pixels," which changes your scaling algorithm slightly so that around the edges it's a bit blurrier and less distorted. Definitely do that if you're not doing pixel art.
Global game options also allow you to choose how your camera fills the screen, so if you're concerned about different aspect ratios consider this.
You may be able to find some DLL's that provide a better scaling algorithm, or use a 3D DLL and use it's scaling algorithm, but I can't really guarantee either.
OR if you're feeling ambitious, you can also create multiple sizes of your Sprites, and, assuming you can get the screen size, use the best fitting Sprite to fit your current screen. This attempt could reduce your distortion from scaling, but uses more memory and a bit of GML. So if you are comfortable managing duplicate sprites, having a larger game file, and using some GML, you could also look into that.
Again, it's been a bit since I've used GameMaker, but hopefully I've put you on the right track.
And don't forget about the GMC! They're a pretty good community, and much more dedicated and up-to-date with Game Maker than this site, so if we can't really help you, you should definitely ask this there.