That's one of my favorite manga, so I'd be THRILLED if they made it into a K-Drama. I would hope it would be set in college though... since all my main picks would seem a little too old for high school, I think.

Here are my personal picks:

Doumyouji Tsukasa: Jae Hee
~Since he's my favorite actor, I just want an excuse to see him all tormented, obsessive, and angry; aka, HOT!!! Besides, he was great in The Art of Fighting, so I know he can pull off the pissed off, don't mess with me, look. Though of course Jo In Sung would be amazing too, especially if they set it in college.

Makino Tsukushi: Yoon Eun Hye
~I can really see her in that role. She'd be cute and feisty, and fit perfectly! Though I'd be just as happy if they decided to chose some lesser/unknown actress... just as long as she fit the role, and could act.

Hanazawa Rui: Jo Hyun Jae
~Even though I didn't like love letter, I thought he played the quiet, nice guy really well, and could really embody that in Rui. Though Im Joo Hwan would work too, especially if set in high school.

Though, really, I'd watch it no matter WHO starred in it. I hope this turns out to be real!! ^_^