Growing up, we always froze our milk. Mom and Dad used to shop at the base commissary so we bought in bulk. Never had a problem with cardboard cartons. Once thawed, shake it up to remix what has separated before opening. If you forget to shake it up, stir well after opening. Plastic cartons can crack. If you are not going to use the whole thing in a day or two, you might want to write the date on it when you thawed it out so you know how many days you have had it. You should not refreeze it once it has already been thawed.
Jean