my ds2 was a fusspot. Strategies that worked for us....
Add only one new element onto the plate. So a couple of cooked carrot sticks, or two or three chips on his plate of sausages and beans.
Just keep doing it, with no expectation of him eating the carrot/chips
Using chips as an example...After several days of the chips being on the plate, make sure you also have chips on your plate and model eating them with enjoyment. Dip them in ketchup or bean juice, and make lots of "Yuuuummmmmmm" noises. But still, no expectation of chip eating from your ds, and no comments or cajolling. The idea is to get them used to the idea of chips as food, and to not get any attention from not eating them.
Next, rope in DH and start a chip race...."who can be the winner eating their chip?" ie a game with the chips(carrots/peas/brocolli etc). Much hilarity should ensure with allegations of cheating, false starts etc. The idea is to put in his mind an association of chips and fun - not pressure to eat. When he joins in, dont make a big deal of the chip eating, make a big deal of the joining in. He will be getting positive attention from "cheating" or beating daddy in the chip race.
You can also play "biggest chip in the world" and make sure he has the biggest chip on his plate for all to admire; "smallest chip in the world" is also popular as you can nibble a chip down to miniscule size.
Favourite teddies in our house have been known to steal chips that wee boys do not want. But they are not very good at sneaking up to the plate. So as teddy sneaks up, dad could be squarking "quick, bear is after your chips!"
Naturally, table manners are not a big priority at this point.
Id also make sure that you have family meals whenever possible, sat at the table, where his not eating is not even commented upon. Get on with family chatting about whatever else, so food becomes family ritual, not a big hoo harr about the right and wrong things to eat -more social IYSWIM.
My son is still fussy, but he has a wide and varied diet and now will accept that he has to eat his veg or finish 3 more mouthfuls of pasta.