Well, humans did discover the Americas via the northern Pacific, many, many, many years before Columbus. The overland and coastal explorations via Asia in the Bering region around 16-20,000 years ago. The exact dates are fuzzy, but this is long before any recorded history and the Bering route was the origin point for the peopling of the Americas. There is some evidence too of later Polynesian contact with the Americas- see /u/b1uepenguin 's answer here for more details. So there were multiple "discoveries" of the Americas that stretch back a considerable period.
As for European discovery of the Americas- the northern Pacific route was not a really viable route for an exploration of the Americas in 1942 1492. The Grand Duchy of Moscow (aka Muscovy)- which is the name of Russia ca. 1492- had not really expanded to the Pacific. This map shows that the furthest extent of Moscow's in the late-fifteenth century was just about to the Ural mountains. The seventeenth and eighteenth centuries witnessed an increased Russian penetration of Siberia, as seen in this map. This expansion was a simultaneous missions for setting up trading missions, bringing the various Siberian peoples under political control, small-scale settlements, and for exploration. Ivan Moskvitin reached the Pacific in 1639 and the Danish emigre Vitus Jonassen Bering explored the sea between Alaska and Asia that would bear his name in the 1730s. Expeditions like Moskvitin's and Bering's were grueling and covered vast distances. The space between Moscow and the Pacific is large and very demanding terrain. Exploring the region was difficult and settling the area was an even greater long-term process.
I have a few answers where I've talked about the Peopling of the Americas and interactions across the Bering Strait here before. TL;DR: Native peoples of Alaska and Siberia have been interacting for millennia. It isn't so much that America was discovered by Siberian peoples or vice versa, as that America was never forgotten when the continents were separated by rising sea levels.
But that begs of question of why that knowledge didn't spread. First, consider the climate. Eastern Siberia does not make for easy travels. The terrain is uneven in many places, with tall mountain ranges proving barriers to travelers even today. Thick evergreen forests can severely impede or even entirely block movement. In the winter, the Siberian interior gets extremely cold--much of the modern day Sakha Republic average -30 degrees Fahrenheit in Winter months. The summer is even worse--while the temperatures are pleasantly warm, much of the terrain becomes swampy and rife with mosquitoes. These problems are exacerbated by rainfall, which occurs rather frequently.
Now consider the distance: The easternmost tip of the Chukchi peninsula is 51 miles from Alaska. Using the Diomede Islands as stops along the way, the journey can be completed with two voyages of only about 25 miles. For the highly maritime boating cultures of the Alaskan coast, this was perfectly possible with kayaks, though it would not be until the development of larger canoes capable of transporting cargo (umiaks) in the early 1st millennium AD that such voyages would become a regular occurrence.
From the Chukchi peninsula to the nearest agricultural societies (along the Liao River in China) is roughly 3000 miles, through mountains, thick forests, swamps, and through territories occupied by highly warlike peoples. The distances to Korea and Japan are similar. Perhaps a journey by boat to Japan is less daunting than an overland journey, but it would still require voyaging through rough seas, oftentimes against ocean currents, and still faced with the challenges of gathering enough food, and not being captured as a slave by any potentially hostile native groups of Chukotka, Kamchatka, the Kurile Islands, or Hokkaido.
In conclusion: For someone from ancient Alaska to reach the civilizations of East Asia would be like Christopher Columbus sailing to the Moon.
Even after the First Millennium AD, with the development of dog and reindeer sleds and umiaks, such a journey would be incredibly daunting. Maybe not "Columbus sailing to the Moon" level challenging, but still "Columbus sailing around the world--twice" level challenging. Reindeer sledding enabled much faster and safer travel across Siberia (especially during the Winter, when any swamps are frozen). Umiaks enabled longer voyages carrying large amounts of cargo. But a voyage to civilization would still be an absolutely Herculean task.
And that leads us to the most important reason the discovery of America didn't spread earlier: Why would anyone undertake that task? Is curiosity of what lies beyond worth travelling across 3000 miles of hostile mountains, swamps, forests, and ocean, just to MAYBE find something interesting? By the mid first millennium AD, trade routes primarily organized by Tungusic nomads enabled Iron, Copper, and Obsidian from Korea to trickle into Alaska, so making such a journey wouldn't have been necessary to obtain these goods.
Similarly, there was little reason for any Japanese or Korean sailors to sail far to the Northeast. The sailing technology was better, but anything that the peoples of Siberia could provide for southwestern merchants--such as timber or sealskins, could already be obtained domestically.
