Pretty fascinating as it really gets down to how the Knights Templar discovered America perhaps hundreds of years before Columbus.
i personally found the "holy grail in america" show to be just a bunch of sensationalist conspiracy theory talk.. 15 minutes of wikipedia-ing shows how out implausible most of the theory that they mentioned is
Sadly, it seems to be the norm these days: http://tvtropes.org/pmwiki/pmwiki.php/Main/NetworkDecay
Farther north east over in Newfoundland is where the Vikings had a settlement and there are some clues up north; Labrador and Nunavut, in the form of stone carvings of hooded monks with Celtic cross symbols.
Add to that the Clovis culture in the eastern USA and I'd say people have been in eastern US/Canada many times over the last few thousand years, before the native people arrived.
I home you meant after the native people arrived.