What does Benvolio mean when he says, “ Compare her face with some that I shall show….and I will make thee think thy swan a crow? Why is he so confident that he can make Romeo forget Rosaline?

Basically Benvolio is saying that he will show Romeo women to make him forget about Rosaline. I think that Benvolio hopes that there will be women at the party which Romeo will like, I don't think that he is certain.