phranque - 9:47 am on Sep 12, 2012 (gmt 0)
does the canonical url point to a document that looks like a customized "not found" page?
Must the content on a set of pages be similar to the content on the canonical version?
Yes. The rel="canonical" attribute should be used only to specify the preferred version of many pages with identical content (although minor differences, such as sort order, are okay).