What did David say to the Giv'onim?
Rashi: He said words of appeasement, and asked them to overcome their Midos (anger) and pardon Sha'ul and his house. Radak (from Yevamos 79a) - since Sha'ul died more than a year ago, it was improper to eulogize him now. Therefore, David tried only to appease the Giv'onim.
Radak: He asked what they wanted to do to [Sha'ul's house]. The verses interrupt to explain their complaint before it gives their answer.
Malbim: He told them that Hashem is angry at Yisrael due to them.
What is the Chidush that the Giv'onim are not from Bnei Yisrael?
Rashi (from Yevamos 79a): They showed via their Midah of cruelty that they do not descend from Avraham, and it is improper for them to cling to Yisrael. David said "there are three Simanim of Yisrael - they have shame, mercy and they bestow Chesed. 1 [Only] one who has these Midos is proper to cling to Yisrael. Radak - David decree d that Bnei Yisrael may not marry them. Even though Yehoshua already decreed, that was only as long as the Mikdash stands - "l'Veis Elokai" (Yehoshua 9:23). David decreed permanently, like it says in Nechemyah (3:26) "veha'Nesinim Hayu Yoshvim ba'Ofel." 2 They are called 'Nesinim, for David and the officers Nasnu (gave) them for Avodah of the Leviyim.
Mahari Kara, R. Yeshayah: Even though they are not from Bnei Yisrael, rather, from the seven Kena'ani nations, Sha'ul should not have killed them, due to the Shevu'ah
Radak citing Yalkut Shimoni 154: They have mercy, for it says "v'Nasan Lecha Rachamim v'Richamcha v'Hirbecha" (Devarim 13:18). They have shame, for it says "u'Va'avor Tihyeh Yir'aso Al Peneichem
When did Bnei Yisrael swear to them?
Rashi: In the days of Yehoshua; then, they made them slaves to cut wood and draw water.
Did Sha'ul merely seek to kill them?
Radak: He actually killed them. This is like "Lehargo v'Armah" (Shemos 21:14), and he killed him; "Lishkav Es Bas Yakov" (Bereishis 34:7), and he lied with her.
What is the meaning of "b'Kan'oso li'Vnei Yisrael"?
Rashi: He put his heart to cleanse and purify Yisrael and do their needs; he wanted to kill the Giv'onim. This Kinah was for the good (concern for their honor), like "ha'Mekanei Atah Li" (Bamidbar 11:29) and "b'Kin'asi la'Shem" (Melachim I, 10:16) of Yehu.
Rashi citing a Midrash: He wanted to kill only the Kohanim. It was a bad Kin'ah, from the day he knew that his kingship will not last 1 , due to the episode of Amalek.
Radak: Refer to 21:1:5:3.
Malbim: Sha'ul wanted to strike them because he thought that they were like rebels against him. Bnei Yisrael continued his decree even when the reason did not apply, therefore Hashem was angry.
Why did he have Kin'ah of the Kohanim? This is not jealousy, rather, desire to punish for sin (helping David). Bamidbar Rabah 8:4 says that he had Kin'ah and hatred of Yisrael and Yehudah, for not revealing where David is hiding.
