。
My opinion is completely different from yours.
Literal
I [of-の] opinion [topic-は] you [with-と] completely differs.
君と (without the contrastive は) treats 'you' as a simple standard of comparison — neutral, factual: 'different from you.' Adding は (君とは) would single you out specifically, often with a hint of contrast against unstated alternatives. Japanese offers several particle combinations for 'different from,' each tweaking the rhetorical emphasis.