My advice, just let the animals work it out.
From years of doing rescue on both cat and dog fronts, I have to politely but strongly disagree. I have seen the results of doing this: dead cats, and dogs missing eyeballs or blinded. We have two dogs on this board whose eyes were damaged by a cat's claws.
There are many on this board (including me!) with cats and dogs who are good friends -- but normally this doesn't automatically happen, it takes caution and time. Please folks, ALWAYS supervise all introductions and keep a watch over all interactions for a good long while after that. In particular, not all dogs can be trusted around cats, EVER, especially adults introduced to cats (much easier for puppies to fit in usually) and it has to be a careful and long term process to make sure they are fine. DO NOT BELIEVE ON THE BASIS OF ONE GOOD INTERACTION THAT THEY GET ALONG AND ARE SAFE TOGETHER. The result if they do not can be a tragedy no one wants to contemplate.
There are fortunate situations in which introductions are easy but
* a cavalier can lose its eye in seconds from a well aimed or even accidentally aimed cat swat.
* cats are generally far more stressed than dogs by introductions and can react more drastically. A stressed cat may go off its food, go into hiding, or worse -- run away and disappear forever -- that is a key reason why anyone with cats should manage introductions carefully, especially if they have cats with access to the outdoors.
* there is no reason to allow a dog to learn by having it clawed by a cat. If introductions are well managed and the dog from the start learns not to chase the cat, then it wil,not come to a situation in which the dog's face could be the wrong place at the wrong time.
* maybe those here who have dogs blinded by cats will come in to comment -- but a lacerated eyeball is NOT something you want to see in your cavalier and is extremely distressing to both dog and owner. So is seeing your much loved cat torn apart by a dog. Do NOT risk it. Make sure they each get the carefully controlled chance to meet, greet, and be trained towards acceptance over time. With luck they will be great friends. But dogs have no innate sense of how dangerous a cat can be and often, vice versa.