Aren't you interested in what it is I want to say to you?
僕 I
君に to you
何を伝えたい what it is I want to say
興味ありませんか aren't you interested in
「君に伝えたいことがある」というのは I have something I want to say to you か I have something I want to tell you で表現できます。
参考になれば幸いです。