I would personally have Dark Pulse (which you can get from the move relearner) on Lucario over Flash Cannon. It gives coverage over psychic and ghosts, and Flash Cannon is only super effective against ice and rock, which Aura Sphere would be much better for.
I don't really see a need for both Strength and Giga Impact. I really don't like Giga Impact as a move, and I would put Earthquake or Brick Break on it. You could probably replace Strength with Return.
Arcanine looks fine. I usually prefer Crunch over Extremespeed, but it's too late for that. But Extremespeed is still great.
There's no need to have Earthquake and Dig on Sandslash. I'd recommend Poison Jab for coverage against grass types, but Gyro Ball, Brick Break, X-Scissor, and Shadow Claw are all also great.
Get Zen Headbutt off of Golduck right now. Psychic is 100 times better due to 100% accuracy, stronger base power, and Golduck having better special attack than attack.