I have 4 cats and 1 dog right now. Now my oldest cat grew up with dogs and I think, thinks he's a dog more than a cat. Now the others I have didn't have anything to do with dogs till I took them in. More than anything it seems to take time for the cat. Now when we brought my Maine Coon home, he didn't get along too well with anybody. I found these collars at Petsmart, calming collars and they work wonders. They have a pheromone and calming herbs in them. For me, they lasted about 2 months. I also used them on everybody when we moved from Ontario to Saskatchewan.
You can find them in with the flea medications etc. I think they're around 14.00 but wel worth it. You can also try Dr. Bach's Rescue Remedy.