There are two basic problems with this scenario.

The first problem is political. The Japanese and the Soviets signed a neutrality treaty in April 1941 that was an ever-present reality for planning in the Pacific. Although neither party truly trusted the other in this treaty, it was clear that the Soviets would not abrogate it while the war with Germany lasted. The stasis between the two powers in northern China suited both parties despite their prior antagonisms. The Soviets received Lend-Lease equipment via the northern Pacific route and this was a supply line they did not want to jeopardize. Additionally, a quiet Siberian front meant less of a chance that it would draw off Soviet troops. Although the notion of Siberian troops defending Moscow in 1941 is largely a myth, the losses the Soviets incurred between 1941-42 were high enough that Moscow did not want to expand the war unless it was on its terms. For its part, Tokyo was satisfied with the Treaty because it meant it could siphon off experienced troops from the Kwantung Army to serve in the ever-expanding Pacific War. Although the numerical strength of the Kwantung Army went up, its quality went down as experienced troops were replaced with Manchurian and other conscripts. More realistically, keeping a diplomatic line open to the Soviets provided a channel for a negotiated end to the war. After Stalingrad and Guadalcanal, realists in the Japanese Foreign Ministry and other parts of the government recognized that the Axis was losing the war and the Soviets could act as a geopolitical counterweight to the Anglo-Americans of Japan played its cards correctly. So long as the Soviets did not desire a war in the Far East and the Japanese did not provide a pretext for the Soviets to rethink their calculations, there was not going to be a violation of the Treaty.

The other factor that prevented the northern Pacific option was geography. Northern Pacific weather provided only a brief campaigning season and added more demands on ships' and planes' normal tempo of operations. Visibility in the region is poor at the best of times and the extreme winter temperatures would have precluded truly mass operations. The Aleutians campaign had shown that the region was tough on equipment. The area was also not nearly as familiar an area as the Central Pacific, or even the SW Pacific to American planners. The famous "Battle of the Pips", where a USN task force engaged with radar echoes because of poor visibility was only the most famous example where the fog of war made this a difficult region to conduct modern operations. American planners did envision a strategic bombing campaign against northern Japan and the Kuriles from the Aleutians. Although the USN and 11th Air Force did conduct air raids against northern Japan from mid-1943, these bombing missions were difficult, and not just because of Japanese resistance. Weather conditions caused a large number of bombers to abort and range limitations meant that there were few truly worthy targets for American air power.

In the end, while some Americans played with the idea of a northern attack route, this was not a viable option. Unlike the Central Pacific, which the USN had been wargaming for the better part of thirty years, the northern Pacific was a relative unknown quantity. Some planners in the 1900s and 10s did speculate on the possibility of a northern drive. The most prominent advocate of this policy was Mahan, who dismissed weather concerns with the idea that "white men thrive in the cold," but he was alone in the upper echelons of the USN. Most of the prewar development of this region was defensive in nature, seeking to prevent the Japanese from seizing it rather than as a springboard for an attack on Japan.The experience of difficulties encountered during the Aleutian campaign further dampened any enthusiasm for the northern alternative. Weather, distances, shortages of ice-free harbors, and the lack of preexisting infrastructure meant Alaska was not a propitious area which to launch a major military campaign.