The most common and most likely answer to this crossword clue is the 4 letter word JEEL
J
E
E
L
More clues leading to the result JEEL
Buddy explains!
The straight part
We know that "frozen state north of the border" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case frozen state north of the border = jeel.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.