This sounds like a tall order for a puppy.
At about 3 months old (when you go on holiday) the dog will have just been vaccinated and able to hold its bladder for no longer than about a hour. It will not be toilet trained and, most likely, not yet trained to 'ask' to go out for a pee.
If you put it in kennels you are essentially isolating it outside, alone in a strange environment. It will undo any toilet training you have achieved so far because he will have to pee in the kennel. It is also likely to cause some social issues, imo. Things linked to the increased stress and anxiety of being left alone.
The other option is to find someone who home boards dogs so keeps them in their house. It is unlikely anyone will accept a puppy who is not toilet trained because of the chances of accidents in their house plus the intensive time required to constantly supervise them.
Following that you need to go back to work. 6 hours is too long to leave a young dog and you should expect this to trigger real anxiety at being left alone - howling, crying, peeing, pooping, chewing. This may or may not be undone as the dog grows up - i.e. it can cause the dog to hate being left alone for the rest of his life.
6 hours is also too long for him to not to toilet and so, again, the dog will have no choice but to 'go' in the house - making it very difficult for him to understand he should, ideally, be toileting outdoors.
In short, this does not sound ideal at all. For you or the dog.
An older dog who is used to being left would be a better fit but you should still cost in having someone come in to see/walk the dog to break that six hours up a bit - that'll cost about £10-15 each day. That £ can add up so this may be an issue.