The Soviet Union was not a threat to Japan in 1941. They had signed a non-aggression pact with Japan, plus at the time of Pearl Harbor they had their hands full fighting Germany, and would not have opposed Japan's planned expansion.
Japan considered the US much more of a threat to their planned Asian Empire. The US had been supporting China in their war with Japan, and the US had cut off trade of vital war materials including oil and scrap metal with Japan.
Now, would it have been better in the long run if Japan had attacked the Soviet Union? Perhaps. Japan could have made concessions to the US in China, thus ensuring we would stay neutral, then attack Russia in the summer of 1942. This MIGHT have been enough help to allow Germany to take Moscow, Stalingrad, and or Leningrad, and forced the Russians to negotiate a peace treaty. If that had happened, Germany would have quickly won the war in Europe, and then could have supported Japanese expansion in 1943 or 44, if Hitler had cared.