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If a page URL has Google Analytics query strings, does the page need a canonical tag? e.g.,

something.com/?utm_source=newsletter&utm_campaign=mar-2013-nsl

I have rel=canonical on all our pages because some of them will be accessed via URLs that have non-Google strings. The strings are only for marketing purposes, not for identifying a specific page to display. e.g.,

something.com/?source=acme

Should I only implement the canonical tag on the pages that might have non-Google marketing strings in the URL?

Thanks, everyone, for the responses. They were very helpful.

I'm implementing landing pages that are optimized for specific keywords. Some of them are substantially the same as another page (perhaps 10-15 words different). Are the landing pages likely to be identified by search engines as duplicate content? How different do two pages need to be to avoid the duplicate penalty?