Actually Alaska to Siberia was a MAJOR route for goods.

The North Pacific is huge, stormy, and a backwater.

As soon as the center of mass for the war shifted South to the Solomon's after Midway and the evacuation/invasion of Kiska and Adak islands there was minimal IJN presence.

In particular many small vessels that were needed for the limited amphibious capacity of the Soviet Navy arrived this way.

The other two major route was first from the UK around and above Scandinavia to Arkhangelsk in Russia. These Arctic convoys were a major battleground in the war. This was the main and largest path.

Additionally was from the middle East and Central Asia particularly Iran by land.

The answer you're after is on Page 29 of Report on War Aid Furnished by the United States to the U.S.S.R., published by the State Department in late 1945.

There were three principal routes (and some secondary ones) to get supplies from the United States to the Soviet Union. The first route used was the northern Russia route, sailing from the United States to Great Britain (or directly, north of Scotland), west of Norway and through the White Sea to Archangel, a port connected by railroad to the Soviet heartland.

This route was problematic. It was vulnerable to German submarines, aircraft and land-based ships (notably the battleship Tirpitz, which gave heartburn to Allied commanders for years). The plight of convoy PQ-17 best exemplifies the problems of this route.

The northern Russia route stayed in use throughout the war, despite military challenges and environmental ones (long daylight in the summer, ice in winter).

In 1942, it began to be supplemented by a route that delivered supplies through the Persian Gulf. Ships left the United States, sailed south through the Atlantic, rounded the southern tip of Africa, then sailed northward to the Persian Gulf.

This route avoided most German interception, but it was long and it arrived at an uncertain destination. Until 1943, there was no reliable rail traffic across Persia, and trucks had to be unpacked at Abadan, reassembled, then driven cross-country to reach the Soviet Union and its railhead at Baku.

Both the northern Russia and Persian Gulf routes took a back seat to the direct trans-Pacific route, however. This was the first route to be used, starting in fall 1941, and it stayed in use every month of the war. No other route can say the same.

At first, American-flagged freighters simply sailed across the North Pacific, delivering to Vladivostok. After Pearl Harbor, American-built freighters were flagged as Soviet vessels and continued sailing. The only difference was their registry. This route delivered 8 million tons of material to the Soviet Union between 1941 and 1945; that's about as much as all other routes delivered combined.

There was the Mediterranean route, used in 1945 alone, which delivered supplies into Black Sea ports after passing Istanbul. In high summer, ships also delivered supplies from the West Coast through the North Pacific and the Bering Strait to the Arctic Ocean. This route was employed for only about three months per year, but it still delivered about 452,000 tons of supplies.

Air routes were also employed. The most famous is ALSIB, a chain of airfields stretching from Montana through western Canada to Alaska. In Fairbanks, Alaska, planes were transferred to Soviet pilots, who flew them from east-central Alaska into Siberia. Of the approximately 14,600 aircraft transferred to the Soviet Union through Lend-Lease, more than half were transferred through ALSIB.

The other half were delivered to Persia, and either shipped in pieces or assembled there and flown into the southern Soviet Union. Barely 10 percent were delivered through the northern Russia route.