When the PlayCanvas engine intializes, it always asks for the back buffer (the main drawing surface) to be antialiased. I guess we could make that an option, perhaps in the Project Settings. But that is only part of the strory.
However, I believe what you should really be doing is to implement this as a post effect. There is already a tutorial on writing a custom post effect. The post effect would simply set a very low res render target up (maybe 1/16th res) and render as normal. That render target would then be rendered to the back buffer with nearest filtering.
It is not really possible to implement crisp upscaling with the resolution settings in your project because that is relying on the browser to scale the canvas and that always applies some blur type filter - this behaviour is not customizable.