I bet if you gave him nothing but his kibble, no treats etc, no encouragement, just ignore him and let him have 15 mins to eat then remove the bowl til next scheduled feeding. you won't have to do any persuading.
But at the same time -- kibble is pretty dull and I would always recommend having something else mixed in anyway. If you are choosing a raw diet and have good chews etc there's no reason he cannot just have the raw patties rather than the kibble. Alternatively I'd give something mixed in the kibble -- well mixed -- most days to add some moisture, along with a little water, for puppies. But puppies just fed kibble *will eat just kibble*, as they were likely fed at their breeder's home. It is natural for new owners to immediately try many new things with their puppy -- and also natural for a puppy to sometimes not want to eat especially in the first few days in a strange place -- and that's when new owners tend to start doing things to induce eating that actually and totally without intention, create a supposed finicky eater.
Many puppies and especially cavalier puppies go through experimenting to train their owners to give them more interesting things each day or to spend lots of time interacting and fussing over them by refusing to eat or selectively eating. They learn instantly that rejecting food gets immediate action and attention from owners! Owners (wrongly in almost all cases as pups can be left to not eat for a meal or two unless there is an underlying health issue) get worried and then reinforce this unwanted behaviour accidentally by trying to tempt their dog to eat with new foods and attention, coaxing -- all the things the pup finds very appealing! It is very common for people to leave their dog at a kennel or with friends explaining their dog has this difficult eating issue and explain how the dog must be carefully fed, only to find the dog eats perfectly happily whatever someone else gives them, in a bowl, right away -- because the dog solely associates the fussing behaviour with the owner.
I have had so many rescue dogs come to me with owners or fosters explaining the dog only will eat from a plate, if kibble is hand-crushed, if hand fed, if fed by a spoon, won't eat kibble... and in every single case within two-three days that dog is eating normally, by itself -- because if they don't, the food disappears and they are usually good and hungry and have ended this nonsense by one or two missed meals later.
A lot of people think the dog is starving and then break down and try new foods, coaxing, just a few treats... and then the problem will continue.
Some pups and dogs are indeed picky eaters, but I cannot stress enough how rare this is and how often the problem does not exist in other conditions than when the owner is doing the feeding. It is a very exasperating problem behaviour and really should be nipped when a puppy or can go on for a lifetime of headaches.
If puppies are not finishing a dish of food it is generally because they are reaching the point where one of their several daily meals can be discontinued. At four months two of mine naturally were ready to move to two and not three meals and started only half eating their midday meal. Some want that meal another two months or so.
If a bowl of food is left at ready access all the time, this encourages a grazer response and is generally not recommended by trainers and behaviourists and vets for all sorts of reasons -- for example, it is very hard with free feeding to gauge if a dog is eating normally (key to catching some serious illnesses early); it can set up serious and potentially dangerous confrontations and guarding behaviour if a new dog or cat is added in to the household; food can go off; it encourages obesity.
Almost all the cavaliers I have known of with true eating problems have had them due to health issues, where appetite can be poor and coaxing a dog to eat can be very difficult.
Slow eaters are a different matter but it is a good idea to see if there's an underlying reason for slow eaters -- such as a decayed tooth or gum problems. Slower eaters should always be fed so that other dogs in the house cannot go grab their food or challenge them for the food.
I feed my four hoovers, including one slower eater, in four corners of a room all under careful supervision til they finish. I have trained the fastest eater to go immediately to sit on the couch so he's out of the way as well.