Are bears and emu prey of lions?

I guess they would if they could! Emus are native to Australia only and Australia has no lions. Therefore, in the current status quo - no, lions do not eat emus. It should be noted that emus possess a unique defence capability, which would aid them if they were in the position of having to outrun a lion. When running at top speed, the physiological structure of their feet enables them to make sudden 180-degree turns which not even a small cat can do: by the time a bigger cat such as a lion slowed enough to make the turn, the emu would be 50-60 metres ahead in the opposite direction.