It would have been a longer and more difficult journey. Partly due to distance, the journey from Japan to California is about a thousand kilometers longer than that from Spain to the Caribbean. And with the technologies of the time (especially for the conservation of food and fresh water) they are no small thing. But above all there was a problem of prevailing winds, essential for sailing. In this Europe is particularly fortunate: the prevailing winds of warm areas, around the Equator, blow from Africa to Central America, from Central America to Japan, from Japan to India, from India to 'Africa. For Europeans it was enough to go down to Africa and then be carried almost effortlessly to America. These winds have been so important for human civilization that they are still called "trade winds" today and the main marine trade routes of the modern world developed on them. The winds that make the reverse path instead blow much further south, around the coast of Antarctica, and much further north. Again Europe is lucky: their "Westerlies" winds go from the current United States to Atlantic Europe, allowing the infamous triangular trade: I bring cheap goods to Africa and buy slaves, I go to America with the slaves and buy precious goods, I return to Europe with the precious goods, all riding in favor of the winds. Instead for Asia it meant going as far as northern Japan or Kamchatka and crossing freezing seas to arrive in depopulated, cold and poor lands such as Alaska, Canada and the northwestern United States.

But the technical and logistical difficulties could have been overcome, had there been the will. Butthere wasn't. Columbus sailed to America in search not of a new continent, but of a new trade route to what was considered the paradise of European merchants: China. Since the times of Rome, Europe has had an enormous hunger for goods from the Far East: porcelain, silk, tea and spices have always had very high prices on the European markets, directing two millennia of trade always in the same way: precious goods from east to west, gold and silver from west to east. To the delight of those who were in the middle: Arabs, Ottomans, Persians and Indians each took a percentage of gold to allow passage over its lands or its seas. Columbus wanted to cut these intermediaries out. On the contrary, China was interested in little or nothing of what came from Europe. No one in China needed to look for new trade routes: she had no need to explore the world, the world going to her.

Someone actually did. Outside your question regarding the great civilizations of East Asia, but it is safe to assume that the first humans in America arrived via boat sailing through the Bering Strait. It would explain the more or less contemporary dating of prehistoric archaeological sites thousands of kilometers away along the Pacific coast, such as those of Meadowcroft Rockshelter in Pennisylvania and Monte Verde in Chile, difficult to explain with the theory of an exclusively terrestrial migration. The big problem with researching coastal settlements 14,000 years ago is that today they are under tens of meters of water, given that the sea level was much lower then than today. The Polynesians also arrived in historical times as far as Hawaii and Easter Island from the islands of Oceania. On a theoretical level it has been demonstrated that it was also possible to navigate, with their boats, from Easter Island to Chile and vice versa, but no traces of a possible Andean-Polynesian exchange have yet been found.