Just because it is correct according to Kant doesn’t mean it also works in Jewish law…

What I mean to ask, seriously, is how the state sells the land of private individuals, or what the agreement between them is.

Moshe, I don’t know whether you are the original questioner (despite the change in nickname, from what you say at the end it seems that you are), but if that is what you meant to ask, then next time ask that. Don’t leave the question on the level of intentions or as a parenthetical remark. I’m not supposed to decipher codes here on the site.

1. If there are two halakhic options, the decision between them absolutely should be made according to the categorical imperative. That does not give the imperative the status to override Jewish law, but it does have moral standing within Jewish law as well. Beyond that, in my opinion it also has halakhic standing, since it is no worse than any other line of reasoning. Especially here, where this is a fundamental line of reasoning regarding all human conduct in the world, and therefore it is preferable to most other arguments.
See in several places on the site about the categorical imperative in Jewish law and in general.

2. I am not familiar with the details of these agreements as they are done today, but in principle the state does not sell the land of private individuals, only its own land. Private individuals can authorize an agent (or the state) to sell their land. Beyond that, the state has the authority to expropriate land, and one could discuss whether that is included here. But I won’t get into that here.
Moreover, because of the Chazon Ish’s claim (which in my opinion is unfounded) that this sale is a transgression and therefore agency does not help for it, Rabbi Goren instituted that the farmer should sell the land to the Chief Rabbinate and it would sell it to a non-Jew (and not as the farmer’s agent). Others are careful that representatives of the farmers carry this out (as in kibbutzim).