Canned corn is not so good because of the salt content.
Scratch is to be used as a treat sometimes: It contains, cracked corn, oats, and wheat berries. It is fairly cheap about 30 cents per pound. It is even cheaper than the canned kind, my place charges $3.00 for about ten lbs, can't beat that one.
People like to serve them a nice portion in the winter before they go to roost so it will help keep them warm at night.
OK? I hope that helps. Welcome, you will be addicted to chickens in no time......
I would not feed 3 week old chicks scratch. It is too hard to digest for the little ones. 3 week old chicks don't need layer either. A little bit of canned corn is probably ok but you will need to give the chicks grit so they can break the corn down. You can buy "chick grit" or some give the little ones finch grit. When first starting them on grit mix a little in with their food for a few days and then give it separate as free choice. Good treats for chicks are hard boiled egg, they love bread but give just a little, fruits like grapes chopped up and melon. There is some place here where you can find a list of good treats.
Maybe someone else can help you find it. I am not sure where it is. And WELCOME to BYC.
Please note that on BYC. there is no dumb questions or dumb answers. I dont give scratch till it gets really cold. You can give other treats such as fresh fruit like strawberries or grapes and even veggies like tomatos.
Corn is high in fat (I think) and they burn a lot of energy after eating scratch. Scratch can lead to problems to. If givin scratch on a daily basis they will stop eating there grower and go straight for the scratch. TI will lead to malnurishment and possibly death