Put the cat in a kennel cage with his food and litter and bed in there. The dog will be able to walk all around and check him out and the cat will see he means no harm, and in three days they will be best (maybe not best) friends.
That's the preferred method to introduce a new kitty to an existing one as well.
The baby gate will not work since kitty will just go to another room and never "meet" the dog