They sell it to the British instead. If both reject it they may try lowering the price or trying to sell it to other nations. The odds of the Soviets taking over would be low given the POD.
One of ideas in previous threads about this topic is that Alaska would be propped up as a refuge state for the White Russians/Romanovs.
But in any scenario in having Soviet Alaska around you can bet that the quantity of weapons that is present on the both sides of Korean DMZ would be nothing compared to this. She and Canadian Yukon would be two giant military bases filled with nukes facing each other.