What does the Torah mean when it refers to bas Shu'a as the daughter of a Kena'ani?
Rashi: It means the daughter of a merchant. 1
Ramban, Moshav Zekenim: In Bereishis Rabah (84:19), R. Yehudah says that twins were born with the Shevatim; Yehudah's brothers married the twins. R. Nechemyah holds that they all married Kena'an women. Perhaps R. Nechemyah merely comes to argue with R. Yehudah, for he holds that a Ben Noach is forbidden to a half-sister, but he agrees that they did not marry Bnos Kena'an, who are cursed. Rather, they married girls from other lands dwelling in Eretz Yisrael, or Amoniyos, Mo'aviyos or from other nations.
Our text of Rashi (from Bamidbar Rabah 2:8) implies that all the Shevatim married Kena'aniyos, but the Ramban shows that it could mean that [only] one of them was a Kena'anis. (PF)
Ramban citing Ibn Ezra: In fact, the Torah writes that Yehudah saw the daughter of Shu'a there, to teach us that, like Shimshon, he went after his eyes and 'fell in love' with a Kena'anis, against the express wishes of his fathers, and it was precisely because he married a Kena'anis that her children were Resha'im and died. See Bereishis 34:2. See also Ramban DH 'uv'Parshas Vayechi'.
Why does the Torah mention that his friend's name was Chirah?
Hadar Zekenim (citing Bereishis Rabah 85:4): Because Chiram, Melech Tzor, who helped Shlomo to build the first Beis Hamikdash, was from Chirah's family, all of whom loved Sheivet Yehudah. 1
Hadar Zekenim: It says three times in the Parshah 'Adulami'; the combined Gematriya is 480, like that of 'Shlomo ha'Melech', because the love lasted until then.
Why does the Torah does not give Bas Shu'a's name?
Malbim: She had not converted. 1
Ha'Emek Davar (2,6): She was not so important. Her father was important; Bereishis Rabah (85:4) says that he was the lamp of the region. Tamar is called by name (verse 6), for she was very esteemed; this is why she merited that the royal line in Yisrael descended from her.
QUESTIONS ON RASHI
Rashi writes that "Ish Kena'ani" is 'a merchant.' Why did he not explain simply?
Ramban, Da'as Zekenim (Bereishis 37:35) #1 Rashbam, Ohr ha'Chayim #1: Because it is inconceivable that Yakov's sons should marry Kena'ani women, whom both Avraham and Yitzchak had strictly warned against. 1
Ohr ha'Chayim #2: She was Bas Ish Kena'ani - i.e. but she was not a Kena'anis.
As the Gemara states in Pesachim, 50a. Refer to 37:35:1:2* and to the Sifsei Chachamim. Consequently, their wives were Mitzriyos, Amoniyos, Mo'aviyos, and the finest of the Bnei Yishmael and the Bnei Keturah - See Ramban. In any event, the Ramban concludes, even if they did marry Kena'aniyos, there is no reason for the Torah to mention it, since that is where they lived, and Adulam was in Eretz Kena'an. And the Torah mentions that she was the daughter of a merchant who came to live there because of his business, because that was why Yehudah married her. Refer to (38:2:1:1).