Google’s John Mueller said in a video hangout at the 3:16 mark that the URLs Google finds in your XML sitemap files are often used to define your canonical URLs. John said “we recommend doing that is that we use a sitemaps URLs as a part of trying to understand which URL should be the canonical for a piece of content.” “So that is the URL that we should show in the search results,” he added.

When you have different signals for what is the canonical, i.e. 301 redirects, rel=, sitemap files, etc – that can confuse Google. But a strong signal is the URL you serve Google in your Sitemap file. John said:

Google strongly recommends you use the final destination URL in your sitemap file, to avoid any confusion.

You can listen to the video at the start time below:

Forum discussion at YouTube.