Untill CrossOver supports 64bit bottles, Landmark can not work.
The patcher (Launchpad) is still 32bit. But the game itself only supports 64bit, and can only support 64 bit as it need more than 4GB RAM.
(When I had the game running during Alpha and early beta it would quickly use up to 6GB RAM. And if allowed could go even higher.
This is a game in development, but it is really fun!
There is a lot of bugs in it and the game is updated frequently witch I understand makes it hard to support as a CrossOver application.
But I really do believe this game is going to become very very popular once in Open Beta and forward.