The only way that Japan can pull this off is with the Siberian Tran Bridge.
Japan sets up a steady shuck into Bury, flooding Asia with INF, ART and ARM. They send a solid WALL of 8 units per turn into Bury, that then march into Yakut, perhaps even to Evenk or Novo. They use a mainland IC (or 2) to provide units to defend in China/Sinkiang and to press through India.
So Japan has 4 TRN, and a defensive capital ship or 2 with their TRNs (BB and an empty AC). They have 8 units in Bury, Yakut, and maybe more to the west of that. 2 FIGs are landed in Bury to support exchanging Evenk/Novo. They may even have a single picket INF in SFE.
Then BAM! Japan builds 3 TRNs and 5 land units in Japan, and uses their existing 4 TRN to empty Japan of the 8 units bought the prior turn to grab Alaska heavy, and WCan with the minimal forces to do the job. The Bury FIGs CAN REACH and land on the AC moved up from SZ60 to SZ63
USA Counterattacks WCan and builds defense.
Then on the next turn, Japan uses the 4 TRN in SZ63 to grab 8 units from Bury, and the 3 new TRN in SZ60 move to SZ63 with the 5 units from Japan and the picket from SFE. WCan is now being hit with 14 units (8 from Bury, 5 from Japan, 1 from SFE) as well as the BB shot, 2 FIGs from the AC (maybe more if Japan had FIGs available to move to Bury in the prior turn, and maybe a BOM also) plus the land units left alive in Alaska.
On the following turn, 8 more units, that were moved back from Yakut to Bury, get shuttled over using the SZ63 TRNs, and the extras move to Japan to grab units for the FOLLOWING turn. You may also have more land units from Japan depending on the prior build, and any TRNs from other areas that can be used to ferry troops from Japan to WCan for the second wave attack. If Japan was able to get a second TRN fleet off FIC with significant land forces in FIC when they pull the trigger on the first wave, the second wave of the attack, the MAIN attack, can easilly have over 20 Japan land units, plus air and naval support.
Anyway, you get the idea.
Might work against a newer player, but once someone has been burned by it, they are not too likely to fall for it again. And if it fails, Russia becomes a BEAR with the Japan pull back to feed the Siberian Tran Bridge.
Oh, and Siberian Tran Bridge assumes negligible USA Naval forces in the Pacific, and negligible USA Air Forces in North America and the Pacific.