g1smd - 11:06 pm on Aug 20, 2012 (gmt 0)

Regarding adding both www and non-www versions to Google webmastertools, may I ask what the benefit of that would be?

Go look at the reports for your site. The answer will be obvious soon enough. :)

Fixing canonical problems from the very first day a site goes live is best done with a redirect. When its for an old site, using a redirect can sometimes mess with the analytics in several ways. The rel="canonical" tag stops that happening.

Although your site is dynamically generated, you'll find that the same page is pulled by Google on different days for www and for non-www and the revisit rate is completely different. That means they will often appear completely different in the SERPs.