Final answer:
Don John prefers being true to his dark nature of a 'canker' rather than pretending to be a 'rose', valuing honesty over flattery.
Step-by-step explanation:
In the quote provided, Don John is expressing a preference for being true to his own nature, despite it being dark and negative, over pretending to be something he's not, even if that alternative would make him appear as a positive and pleasing character.
He would rather be a canker in a hedge, representing something harmful and unwanted, than be a rose in someone else's eyes, indicating beauty and desirability, if that means compromising his honesty.
Therefore, the essence of his statement is that he values plainness and honesty over flattery and deceit.