Welcome to the Q&A Forum

JavaScript is client-side code that's generally rendered in browsers, which means Google crawlers typically won't see it, and the almost definitely won't process it for these kinds of directives. You can create these tags dynamically, but you need to do it with a server-side scripting language, like PHP, ASP, etc. That's a common practice, and many large sites dynamically code canonical tags, META ROBOTS, etc. (I've done it on many sites).

As Adam suggests, responsive design seems to be the preferred route at the moment. This is different in that you have a single URL for everything. Whatever platform the end-user users all content is sent to their browser and then it is rendered differently for different devices. This requires a slightly different mindset as you are effectively building one version of a site, but changing the way it appears to different users.   Therefore, if you want a "stripped down" version of the site then it is best done by serving up different navigation. However - if you are committed to desktop/mobile versions of the site and they are utilising the same content then I would use a canonical from teh mobile to the desktop site. I think that the domain choice is pretty subjective. I'd prefer m.domain as it is less likely to get confused with your overall site structure. However, if you are not yet committed down one path and the intention is to serve the same content - definitely look at the responsive option.