I can't remember if someone's done this before, but I had the idea and I whipped up a quick map to illustrate.
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Something I realized about the New World in OTL: It's very east-oriented. The Atlantic is much smaller than the Pacific; the Pacific may have more accessible islands that are useful for navigation, but these are limited to the southern hemisphere. Once you get to the Americas from the west, you have to deal with a long chain of mountains and highlands from the Andes to the Rockies; a temperate coastal seafaring culture wouldn't have much to work with on the west coast except in California, and if you travel east from there you only get desert and mountains. By contrast, if you approach from the east, you have a temperate, low-lying eastern seaboard, massive navigable waterways in the Mississippi and Amazon rivers, fertile plains from Argentina to southern Brazil, and some of the best wheat-growing land just south of the Great Lakes.
So I flipped it. Now, if anyone tries to use Columbus's route, they'll probably starve before finding land. On the other hand, explorers from East and Southeast Asia would have a much easier time crossing the Pacific.
The Americas in this world have a different climate than OTL. The entirety of Quebec is fertile and has decent soil in a temperate belt that extends through Hudson Bay out to Lake Winnipeg, with about as much arable land as the entirety of Europe. The Northwest Passage is actually ice-free and navigable for around half the year. The area from Cape Cod to Delmarva has a decidedly Mediterranean climate. The stretch from North Carolina to Florida and the entirety of the Gulf of Mexico are varying degrees of desert; the sheer size of the Mississippi basin keeps the river flowing throughout the year, though it does have seasonal floods not unlike the Nile river. Mexico's pacific coast is a desert. The Caribbean is largely unchanged, as is Central America.
The Amazon Basin is still rainforest, but not quite as wet as OTL. The very tip of the continent, around Pernambuco, is tropical savannah. The Andes cast a massive rain shadow, making the southern half of Brazil and the northernmost part of Argentina a desert; even Australia is somewhat drier due to their influence. However, the Argentine and Brazilian coasts remain temperate, mild, and fertile. Patagonia is lush, temperate, and rainy, a bit like England. On the Atlantic coast, things are a bit different; the southern half of Chile is more or less desert, but the stretch from Valparaiso to Cali in Colombia is extremely rainy; all the moisture from the Atlantic trade winds are blocked by the Andes and is dumped on a few kilometers of coast. In North America, Baja California and Sonora are both lush monsoon rainforests reminiscent of Vietnam, and Cabo San Lucas is one of the rainiest cities in the world. SoCal is extremely humid, not unlike Guangzhou, and the enormous California Valley is probably even more fertile than before, though a bit cooler. Far northern California to Oregon is cool and temperate, comparable to OTL New England, while Washington is more like the Canadian maritime provinces. BC and Alaska are as cold and uninhabitable as Sakhalin and Kamchatka.
In considering cultures, I'm putting up a massive butterfly net to keep individual culture groups recognizable.
I imagine in this world East and Southeast Asian explorers would find the new world more accessible and attractive than European ones as in OTL. The Chinese or Japanese would eventually settle the Saint Lawrence waterway, which would become one of the most productive wheat-growing regions in the world, while rice would be more intensively cultivated around Delaware and Tidewater. Malay and Indonesians would discover the Brazilian coast, finding the Amazon region favorable to grow bananas, coconuts, and other tropical fruits.
The strains of corn that become popular in North America in this timeline would be hardier and more drought-resistant, as it would have been spread to the desert civilizations of the Mississippi before making its way to the Pacific coast. Potatoes, on the other hand, would be essentially unchanged.
The exchange of diseases would still heavily favor the Old World, perhaps even more than it did in OTL, but it would be interesting to see how the traditional Chinese model of tributary state networks would interact with the natives as opposed to the European model of conquest and subjugation.
In this TL, I imagine the largest cities would be in the central Mississippi river, mirroring ancient Egypt; whichever culture becomes dominant, the center of power would steadily migrate towards the mouth of the river, as this would have the most consistent flow of water. The Mesoamerican civilization would probably be centered more on the Uto-Aztecans such as Huichol in the South and O'odham or Paiutes in the North, rather than the Mayans that dominated in OTL. The Inca and other Andean civilizations, defined as they are more by altitude than anything else, would likely be more or less unchanged. Historically, the Chinese settled as merchants in places where there were already established cities, so I imagine they would congregate most heavily in the Mississippi river area, where there would be a robust trade network, the Colorado River region, where there would likely be complex civilizations that could trade in silver, and in the Andes, where they would also have silver. Before long, however, these cities would be struck by an onslaught of diseases, which would disproportionately affect natives and leave the merchants relatively untouched. It would be interesting to see how this dynamic - of traders looking to profit faced with the deaths of their trading partners - develops from there.
Europeans would spend a few centuries convinced that nothing of value exists in the Americas. They would become familiar with Alaska, perhaps, but considering it's even colder than OTL that might work more to its detriment than its benefit. Instead, Europeans will continue to focus on trade with India and Indonesia. However, without the influx of gold and silver that comes from the New World, they would find it more difficult to achieve the ascendant position they did in OTL. As ships become better built and are able to travel farther, they'll eventually make it to California, probably before the mid-1600s, where religious minorities would be attracted and eventually settle. However, the mountainous terrain would still discourage further exploration inland.
