I think the opposites in “Leda and the Swan” are the fact that Leda’s rape is both pleasurable and un-pleasurable action. It is pleasurable to the Swan (Zeus) because he is having sex with Leda and getting what he wants from here, but of course it is un-pleasurable for Leda because this is happening without her content. She is unable to stop it and ends up pregnant from the rape as well. Another antithetical element I notice is between the poem and the painting. In the poem the Swan (Zeus) is described with such strength; “…the great wings beating…”(1)/ “…her thighs caressed”(2)/ “…her nape caught in his bill…”(3). In each of these lines the words “beating”, “caressed”, “nape caught in his bill” tells us (the readers that the Swan is rather large and strong. Leda cannot handle the strength to prevent being rapped. In the painting Leda is much larger than the Swan which is the complete opposite of what the poem describes for us.
Not sure if this is correct but I tried.