It's all but certain. The Japanese declaration of war on the US was never an end in itself, but rather the means to an end: to secure their oil supply to prosecute the war in China. If the USSR sides with Japan (heavens know why; perhaps everyone in the Soviet leadership up to and including Stalin himself has a collective aneurysm and their replacements decide that a militant, aggressive power annexing border territories they have their own designs on is jolly fun), it only makes Japan even more likely to insist upon the historical Southern Resource Area rather than the Northern Resource Area (Siberia). With Barbarossa, the USSR is going to need all the oil it can get for its own use; it won't be able to meet the copious needs of the Japanese. The attack on Pearl Harbor and invasion of the Philippines are intended to keep the US occupied and away from the real war with the British and Dutch, behind a cordon of island fortresses from which the Japanese can exercise a defense in depth while the US are forced to operate from across the Pacific (a more successful Pearl Harbor aids with this). Unless the British can be absolutely relied upon to throw the Dutch to the wolves (which the Aussies and Kiwis would protest vehemently, if only because they don't want the Japanese as neighbors either), Japan can't trust their military bases in Singapore and Malaya to stay out of the conflict, and thus will need to embark on a first strike there just as they did in Pearl Harbor.
By the same token, the timing of Pearl Harbor has only an indirect relation to the Sino-Japanese War: to wit, the US oil embargo on Japan as a consequence of that war. The surprise occupation of French Indochina was icing on the cake, so to speak, but the oil embargo was key. The Japanese, before the attack, offered to withdraw from the southern piece of Indochina in return for a complete end of US assistance to China, US supplying free oil to Japan, and assisting in acquiring materials from the Dutch East Indies, a proposal the US did not seriously entertain for obvious reasons. It doesn't matter if Germany or the USSR backs China or Japan; the US oil freeze spelled an end to Japanese imperialist ambitions and thus made a war necessary within the year. Alternately, the Japanese could have seen reason, backed down in China, and accepted a peace with some concessions, but that would require the Japanese leadership at this stage to be reasonable.
Also, if Japan and Germany both realize it'll be a long war, they're much less likely to embark on it in the first place. They both need a short war if they want to win; they lack the manufacturing (Japan) or resources (Germany) to win a long one. If they expect a long war, they'll be aware they'll be unlikely to win. Neither power is outright suicidal (certain statements by the Japanese leadership aside). That said, if they do make provision for a long war, they might be able to fight better and harder for longer; Germany begins to gear for total war before 1942, for instance. Neither, however, is likely to actually win; they're now planning for a war that plays to their opponents' strengths, the sort of war we actually had. What Germany needs to win is to knock the British out in 1940 or 1941, avoiding the blockade that cut them off from imported supplies like oil, rubber, and tungsten and possibly (though unlikely) even tying British and US hands regarding the USSR come Barbarossa. What Japan needs to win is to secure the DEI and immediately come to terms with the US and UK that leaves them cemented behind a sanitary cordon with a free hand in China; Yamamoto's "six months to a year," in other words. What it ends with, likely, is a 1946-1947 war with nuclear craters in Berlin, Hamburg, Munich, Dresden, Hiroshima, Nagasaki, Kokura, Tokyo...
EDIT:
Oh, and regarding USSR backing Japan. Likely, the USSR conveniently "forgets" to declare war on the US along with Japan, being thoroughly occupied with Germans in the Soviet heartland, and the US, seeing the USSR keeping Germany busy as well (FDR always thinking of Nazi Germany as the primary threat), conveniently declines to declare war on them as well; it's not like the USSR attacked Pearl Harbor, after all. Even if we go further and say Lend-Lease to the USSR ceases, they still stop the Germans cold and gradually push them back. However, the war years are marked with a much slower grind back westward (shorter logistical tail for the USSR without those trucks, jeeps, railroad engines/stock, or fuel) and severe famine (likely encouraged by the Germans as well, who are stealing everything they can to stave off famine back home as well). What likely occurs is a more difficult post-war layout, as well, without Yalta or Potsdam - perhaps a united Communist Korea (as the USSR takes "protective custody" of Manchuria and Korea anyways) and Communist Greece, perhaps a united Allied Germany. It's hard to say.