Answer:
A hyperbole is a figure of speech where the word choice is greatly exaggerated to emphasize the impact or meaning.
EX: I'd love you for a thousand lifetimes.
^
While obviously not, the exaggeration emphasizes my meaning.
A hyperbole in the poem could be "Till a' the seas gone dry..."
Burns emphasizes that he will still love thee, even when the seas dry up, which both acts as a metaphor and hyperbole.