oooo this could be a can of worms.
You could point to the crossing of the bearing strait in the 12,000 or so BC of the Eastern Asians as Tom mentions above.
Another much argued over theory (which has gotten fuel from recent excavations off the east coast and possible DNA research) of the Soluntrean's. the Soluntrean's originated from France during pre-historic times.
The Vikings settled in Eastern Canada in about 1000 - Lief Erikson.
There is a settlement in TN that was settled, as the story goes, very early. They were from a protuguese shipwreck off the coast of South Carolina. They worked their way to TN and were discovered in 1690. They had been living there for a long while prior to discovery.