Hi, I'm a hairstylist...
Have you thought about popping to the salon you mentioned and introducing him to the stylist (maybe even a few times) so that they - and the surroundings are familiar? Salons can be weird places to LO's, they smell and noisy, also we teach them from early on that scissors are dangerous and not to touch that it may be scary having someone come at you with them. I used to have kids that loved having their hair cut, so don't presume he'll hate it, just ease him into it. HTH xx (Good luck!!)