**This reply is not intended as a Psak Halachah but rather as an exploration of possible Halachic solutions to the question posed.**

Let's answer your questions in the order you gave them.

1. Kena'anim

The term "Kena'ani" used here in the Gemara, may or may not apply to an idol worshipper, but it does not apply to a person from the nation of Kena'an. The Gemara (Berachos, 28a) tells us that the Emperor Sancheriv when he conquered the Near East, wiped out the national identities of the people he conquered. He did this by exiling them from their native lands and replacing them with other peoples, as he did with the ten tribes of Israel. This all happened long before the formulation of the Mishnah and Gemara. Therefore the Halachah here is not referring to Kena'anim but rather to non-Jews in general. In fact, there are texts of the Gemara, which use the word "Nochri" in place of "Kena'ani". The Rambam also, when he records this Halachah in the Yad Chazakah uses the term "Nochri" instead of "Kena'ani". We find the use of the term "Kena'ni" in other areas of Halachah used to refer to non-Jews in general, such as Eved Kena'ani, which refers to a non-Jewish slave. In short, Kena'anim don't get any unique treatment when it comes to returning lost objects.

2. Other idolaters

The RAMBAM and the Shulchan Aruch (CM 266:1) do not make a distinction between idolaters and non-idolaters. In neither case is one required to return the object. There is, however, one opinion among the early authorities - that of the ME'IRI - that makes some kind of distinction. He says that those that follow a religious system that imposes some kind of moral code upon its adherents must be given the same treatment as Jews. The distinction is not, strictly speaking, between idolaters and non-idolaters, because the ME'IRI was almost certainly including Christians among those who must be treated equally even though Christianity is theologically problematic regarding the question of idolatry.

(I should mention that, while the RAMBAM makes no distinction in regards to the obligation of returning the lost object, he might make a distinction similar to that of the ME'IRI, in regards to the prohibition of returning it. See the commentary of the Be'er ha'Golah, CM 266:1, note 2.)

3. Non-Jews who are not idolaters

See 2.

4. Non-Jews who fully comply with the laws of Bnei No'ach

I am not aware of any authorities that give special treatment to non-Jews who adhere to the seven laws of Bnei Noach.

5. Non-Jews living in a country whose legal system requires the return, when possible, of all lost objects.

The question is whether the concept of Dina de'Malchusa Dina (the law of the land is binding) applies here or not? This is a very good question. Let us start by mentioning a basic Machlokes Rishonim regarding how far this concept can be applied. The SHILTEI GIBORIM (Bava Basra, ch. Chezkas ha'Batim) holds that it only applies to things which are Hana'as ha'Melech (for the benefit of the king) such as taxes and expropriating property. The MORDECHAI (in the name of Tosfos, Bava Kama, ch. ha'Gozel Basra) holds that it applies in all areas of civil law. (The question is how to understand the phrase: Dina de'Malchusa Dina? The simple understanding is that the law of the king is the law. This, in fact, is how the RAMBAM (Hil. Gezeilah, 5:11) translates it and this would be in line with the MORDECHAI. The RAN (Gitin, ch. 1) however, says it means: a law relating to the kingship is the law. This would be consistent with the Shiltei Giborim.)

According to the Shiltei Giborim it is clear that a Civil law requiring the return of lost objects could not override the Torah law which says that one is allowed to keep the object and in fact, it might be forbidden to return it. The question is what would the MORDECHAI say in this case? The REMA (CM, 259:7), quoting the MORDECHAI, says that even though the Torah does not require one to return an object that was washed away in a flood, nonetheless because of Dina de'Malchusa Dina, he is required to return it. He also says (356:7) that one is required because of Dina de'Malchusa Dina to return stolen objects even though there was Yei'ush, even though this contravenes Torah law. It seems from here that if there is a law to return lost objects, then we must obey it.

The SHACH, however (356:7, note 10), commenting on the case of the stolen object, says that the real reason we must return the stolen object is because the Minhag of the Jews is such and not because of Dina de'Malchusa Dina. He elaborates on his opinion in another place (CM 73:14, note 39) and says that we never apply Dina de'Malchusa Dina when it contravenes an explicit Torah law, only in cases where there is no existing Torah law. The KETZOS HA'CHOSHEN (CM 259:7, note 3) proves that even the REMA did not mean to apply Dina de'Malchusa Dina in the full technical sense of the concept, because he himself says that the requirement to return the lost object only applies if the person is wealthy, but not to poor people. If Dina de'Malchusa Dina was the operative factor here, there would be no distinction between rich and poor. In addition, the REMA himself writes (CM 369:11) that a law regarding inheritance cannot override Torah law. (He does, however, qualify this statement by saying that if it is for the benefit of the land, then it can. The SHACH (CM 73 above) argues with him on this point and says that the source of the REMA, a Teshuva of the RASHBA, makes no mention of this qualification).

In short, it seems from most of the Poskim that a law issued by the government requiring the return of lost objects would not be binding because it contravenes Torah law.

Kol Tuv,

Yonasan Sigler