Without sound recordings we don't really know a whole lot. Interestingly enough, we often think that early Americans would sound British, but we also don't actually know what Brits sounded like back then either. It's safe to assume that they have migrated too.
The best way to make a guess is to find isolated populations, but then, they have probably evolved too. There's another thread here on early American accents, where I posted the link below. There are familes that have lived on isolated Chesapeake Bay islands (reachable only by boat) in Md and VA since the 1600's. People have moved off the islands (they probably hit their peak population 150 years ago) but it's been rare for anybody to move in. The speech of those people has long been known to be archaic and to date back to the 1600's, but, since then it has evolved to suit jobs that mostly have to do with living on the water, harvesting shellfish and fish, so we don't know for sure how it originally sounded. Some linguists have speculated that the accent may actually resemble Shakespeare, since these people's long lost ancestors came from the same part of England, but that's just speculation. It's worth a listen for the pleasure of hearing a real antique American accent. Some of it barely sounds like English.
[ame="http://www.youtube.com/watch?v=AIZgw09CG9E"]The odd accent of Tangier VA (from AMERICAN TONGUES) - YouTube[/ame]