I'm afraid I also don't understand why you want to display your game this way. If you set up your game right, it will show everything at a 16:9 ratio and crop off the sides at 4:3. It looks far, far better this way than stretching the canvas out of proportion and it works on all aspect ratios, even if it takes some extra work to set it up. Why don't you want you use this method?
Also, console game makers have to deal with different aspect ratios too. They don't just render at one resolution for all TVs. In fact, I'm pretty sure console manufacturers wouldn't even allow it if someone tried. The ps3 for example has a setting in the video options to select 4:3 or 16:9, and devs have to make the game's HUD and such work with both, as it's very unprofessional looking to stretch the image like that, which is why they don't do it and render at a different resolution instead (also, the resolutions console games render for widescreen content at is actually generally something more like 1024x720/1152x720 from what I've read. Regardless of what they use, they still keep the image proportional).
If you really don't want to deal with it at all, you can do what final fantasy dimensions and such do, having it in full screen letterbox mode and having black or colored bars at the top and bottom of the screen, since people are often used to that from movies (even 16:9 screens have black bars often because movie content often uses a wider aspect ratio than 16:9).
Arima Look, I was experiencing this for 2 months, so you have to trust me with sincerity. I'm going to respond, so do not take it as offense.
We know that everything you say is an excuse to not have interest about it because you do not know how to solve the problem of others, this is your personal opinion against the client's needs, we do what they want and expect to see the results as things go, if you say, is very unprofessional for this style I'm afraid you are wrong. This is game design and sometimes we just limited. You didn't mentioned on resolutions for phones. No need to be presumptuous to say so even if you published a game with multi-resolutions, I see you have no experience in that.
What you say about can not render a resolution for TV is true, but is different because HTML5 would not need to manipulate to change video resolutions from operating system you are using current resolution, it should work at any resolution.
There is a demo Fullscreen example does not show the true fullscreen it still has black spaces, is a hindrance to the experience. Not a movie work, is a work of video game. Because videos can not be drawn via programming. Someone teach me to full screen without black spaces and the sprites must be shown outside the exact layout of window design.
Let me show you an example you said stretching is not very professional, they look at that and judge for you. There is no perfection.
http://i.imgur.com/6dLtua3.jpg
(This image is very big...)
I'm saying that Scale can be useful for other game design, but also we need a more option.
Many developers we still need the option as stretching the screen to fit, that has the issue we're seeing of stretched images. It is normal if we have assets of 1024 x 768 to 1024 x 600 platform, using stretching so it would look fine without problems.
From a high-level perspective, depending on which is more important, maintaining a consistent aspect ratio, or ensuring that no one to see more than someone else just because doing lot wider screen or workshop.
Three important options are: letterbox, cropping and stretching.
Devices can choose on whatever resolution they feel like. Creating Project with each different to specificed platforms would be big waste of time, we might Consider having a stretchable or tileable graphic for the background (very huge! CocoonJS does not support extreme huge sprite, however it might use power of two tile could work), and maintain the same effective (scaled) playing area.
I'm going to ask you to support the idea to solve the problem of others and demonstrates C2 is useful after all, on the contrary would be useless and despised!
Don't forget about low resolution may take advantages all of them render the game and let the GPU doing the process. It helps boosting the FPS and save memory in most cases.