Jem Schofield put together this video describing how to sync external recorded audio with HD video shot on the Canon 5D Mark II. The 5D Mark II records audio from a built-in mic, but for improved quality Jem uses the Zoom H4N to record audio from a shotgun mic.
He then goes over his process for syncing audio tracks quickly and easily with a plugin for Final Cut Pro called PluralEyes.
Visit the theC47.com for more video tutorials by Jem Schofield.