I just recently completed a project where I integrated Marketo and Google Analytics. I published an article and accompanying cheat sheet, both are available from Google Analytics-Marketo End-to-End Integration - as someone suggested, there are a ton of threads on this topic... but sadly very few real answers. You will find examples and step-by-step instructions in my cheat sheet.
I recommend you start by searching for the tons of old threads on this general topic. Then post back with specific questions or details, as "integration" has many meanings. Remember first of all that Marketo has its own analytics package (Munchkin) which is not as full-featured as the whole GA suite but which has the extremely powerful advantage of linking directly with your lead database.
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