。
My opinion is the opposite of yours.
Literal
I [of-の] opinion [topic-は] you [from-とは] opposite is.
The contrastive topic marker は stacks onto と to give 君とは ('from you, specifically'), marking the person rather than the opinion as the standard of comparison. The framing differs subtly from 君の意見とは: this version says 'opposite from you,' while the alternative would say 'opposite from your opinion' — close in meaning, but the focus shifts from idea to person.