I have a dog and a cat will they ever get on with each other?

It depends if they grew up together or not.

If they did not grow up together then you need to spend time with both of them to get them to know each other well.

I had the same situation and the answer is yes just stop guarding them you need to let the cat get his bluff swing in witch is basically shhowing the dog that I can hurt you if u hurt me leave them alone STOP GAURDING THEM! OR THEY WILL NEVER GET ALONG!

It really depends on how they are reacting now. Can you give more detail?

Is the dog being aggressive towards the cat or just chasing or being pushy?

What breed would also help as well, breeds like sight hounds generally don't get along with cats as they are bred to chase, while other breeds like toys will be more inclined to get along.

Training will differ depending on the situation.