Oh boy. This is a subject worthy of a PhD thesis on it's own, let alone a reddit post. Where's /u/Taiko when you need him?

The short answer: Maybe.

The long answer is well, we're not really sure. It kind a depends heavily on what you mean by "medieval manor system". The sterotypical manor system that is taught in high school history textbooks usually looks like this image from a historical atlas published in 1923: http://en.wikipedia.org/wiki/Manorialism#mediaviewer/File:Plan_mediaeval_manor.jpg

The idea of a "manorial system", like other aspects of "feudalism" (note the scare quote!), is really based in some ways on 18th-century historiography of the 11th century in France, combined with 20th century misunderstandings of both. That is to say, so-called "manorialism", like other aspects of "fedualism", never really existed in the ways it's usually depicted in the high-school or college history textbooks, and is largely based on an overgeneralization of a very specific set of social and economic circumstances that only ever really existed in Northern France and Southern England during the period c. 1000-1200, and maybe not even then. /r/AskHistorians had a very insightful AMA about this a few months ago: http://www.reddit.com/r/AskHistorians/comments/2bs0rc/ama_feudalism_didnt_exist_the_social_political/

So, with that out of the way, it its clear that in Northern France (aka Northwestern Gaul) there was not a large demographic discontinuity in Late Antiquity that is seen in some other places. That is, the locations of a great many medieval villages and manors, and castles in medieval France were inhabited more or less continuously since Roman times, and sometimes the later medieval manor houses and abbeys were built right on top of the exact site of the Roman-era villas. Whether this indicates a substantial degree of continuity in economic and social systems between the Roman Gaul of Late Antiquity and the Kingdoms, Dutchies, etc of Medieval France, is a question still being actively examined by modern archeology and historical scholarship. I don't feel qualified to pass a judgment on the topic, although I will recommend Stephen Dyson's The Roman Countryside , published in 2003, as a great book on the current understanding of the social and economic landscape of rural communities in Roman Gaul right up through the period you are interested in.