The challenge is to get a major military and/or commercial highway connecting Alaska and Siberia built between 1945 and 1991.
Based on infrastructure logics and your political PoD which cities would it connect?
Rule: Both the USSR and the USA must remain communist and capitalist respectively
Given that there isn't a 'major military and/or commercial highway' between Alaska and the lower 48, nor, on the Soviet side, to the Bering Strait....
I could see a weird WWII situation where the US, simply looking at a map, and not worrying about weather, decides to attack Japan along a northern invasion route in addition (or instead of) the Central Pacific and South West campaigns.
So the AlCan Highway gets built, firstly, and a seaport is built at the mouth of the Yukon (goods brought up through Canada are either floated down the Yukon in the summer, or pulled on the ice, in the winter). With a rail / highway option progressing from that port back to eastern Alaska on a lower priority
Meanwhile, <handwavium> the Japanese don't allow US shipping to go through to Vladivostok. Since most LL to the Soviets was carried on US ships, this is a problem. So the Soviets start building rail / highway through Eastern Siberia to a new port north of Kamchatka.
Well, of course, the war's over before all the infrastructure's in place, but it's well under way, and bureaucratic initiative means they get completed.
Then, later, in the ´60s, Krushchev (or equivalent) normalizes relations with the West, and in a great show of unity, make an announcement on the Diomede islands about the trans Bering Highway/Rail connexion.
(Two announcements - one on Big Diomede and one on Little Diomede, one in Russian, one in English.)