OK, obvious POD:
Viking settlements in Vinland (OTL Newfoundland) survive. They are eventually cutoff (by 1300 or so) from Norway, and sink into legend in Europe, but survive.
Massive hand-wave: European age of exploration proceeds as in OTL. The Spanish hear rumors of a white-skinned settlement to the far north, but absent any accompanying rumors of gold ignore them until about 1575, when the first 'Viking' raiders hit the Bahamas. It's like something out of a bad dream - the Vikings come storming in, whooping and hollering, happily having made use of Native American weapons like tomahawks, and inflict a lot of damage.
Sir Francis Drake is intrigued by the Vikings, and journeys to Newfoundland, 'discovering' them. After some skirmishing (more to prove English manhood in the eyes of the Vikings), an accord is reached; the English provide guns and other modern weapons, the Vikings agree to only raid the Spanish.
It works for a while; eventually the Spanish get annoyed enough to send a fleet up and burn some Viking villages; but the English get an earlier toe-hold in North America, and beat the French to Quebec (the French focus on South America - OTL Argentina and Chile). The Vikings become allies of, and then subordinate to the English (later British) kings, and a state in the USA when it becomes independent ...
Mike Turcotte
You. Start writing books set in this universe. Right. Now.