This is far, far outside the scope of a normal Mythic Europe campaign... Art & Academe mentions that going too far north or too far south will cause things to become very weird as you approach Here Be Dragons territory. About the furthest west any particular part of the setting goes is the Canary islands, aka the Purple islands, aka the Hesperides. Going Far East is its own kettle of fish, which would require making an entire expansion and go far outside the scope of Hermetic theory- but even China or India are at least vaguely known of in 13th century Europe. But "The New World" got its name because Europeans didn't even know there was a continent there until centuries after 1220 AD! Sure, the Vikings raided the east coast of North America that one time (and lost), but Hermetic magi aren't on speaking terms with Vikings.
So, to GMs out there... in YOUR campaign, how would you handle very insistent players building a nigh invulnerable, well-provisioned sailing ship with a healthy, non-mutinous crew and sailing as far west as they can? Would they literally end up in East India instead of encountering West "Indians"? What would a Mythic Europe version of the Americas be like? Is there any way to model the HUNDREDS of different First Nation spiritual beliefs with game mechanics in a way that isn't insulting? In fact, is this even a good idea?
Why would there be a problem with talking to the Vikings. If you just do some gooling and reading you will see that they traded more then they plundered. And they traded basically all over Europe. As far as India.
So having vikings trade with your troupe would not really be a issue. Also they had pretty awesome maps. So why not have the vikings sell them a map of the new world if you want them to go there.
I like a here there be dragons feel. I would probably go more and more fantastic in nature. I'd make things up out of whole cloth. My stuff in the far west wouldn't look like north America or anything else (unless the players really were looking forward to that).
sub rosa #19 p.19ff Roanoke, Founded has time-lost Elizabethan colonists ready to appear in an Ars saga.
sub rosa #19 p.30ff The Friends of the Apacei of Vinilandia are a Mystery Cult of magi very much interested in Vinland.
In one game I used it as where the few surviving Diedne had gone and started to rebuild themselves.
I've had the Diedne turn up with Aztec warriors, and Flambeau Magi lead the Spanish invasion.
In a series of live roleplaying events (set across several years and consecutive tribunals, culminating at the Grand Tribunal) in which I played, some of the characters eventually fled from Europe on the ship of a probably-insane Verditius heading west. In the after-game summing up, it was generally decided they probably reached a "Mythic Americas" and attempted to set up a more 'high fantasy' mage-ocracy in Mexico just prior to the arrival of the Aztecs. The likely success of this operation was left to the imagination of those who played those characters. One player commented: "I think we should call the setting VisPunk".
In terms of modelling the hundreds of First Nation beliefs - don't. The thirteenth century is part of the Medieval Warm Period, so the same favourable climate that allows the Norse settlements in Greenland also allowed the building of large settlements along the Mississipi, so fill your Mythic America with city states of mighty and proud natives capable of repelling any mundane invasion.
I'm looking forward to seeing how 7th Sea will handle the New World in their new settings books, as they have a good track record of creating fantasy versions of history that have the more contentious and offensive parts smoothed over.
If I was running a campaign where people went west, they would discover that they hit a series of never-ending Faerie Regiones, unless they figure out a way to bypass the fae upon which they end up in the Indian Ocean.
I'm thinking back to Realms of Power: Magic and how it mentions Prester John's Kingdom being real, but buried deep in the Magic realm... A Faerie regio might be a good option, but I also like the idea of the players finding something, well, "real". Maybe there really is a promised land out there- though, you may regret finding it...
The current campaign I'm in is set in the Colorado mountains - reached by a portal that was a viktir rune pillar pillaged in some archmage's history (and then studied, left on a shelf, rediscovered, and re-studied) that was originally opened up in France, but due to accidental time travel shenanigans by the PC's now opens up in the middle of Iceland instead.
It's currently a high-magic setting, with the whole concept of Realm-aligned magic being a bit more fluid than in Europe.