Why did the Spies make a point of mentioning Amalek, who was not even one of the seven Cana'ani nations?
Rashi: Because they had already been 'burnt' by Amalek, so they mentioned them in order to frighten them.
And why did they mention specifically the tribes that they did and the four areas where they lived?
Rashi: Seeing as the mighty Cana'anim lived right next to the River Yarden, they would not even be able to cross it to begin the conquest of Cana'an.
Ramban: He mentioned these mighty nations, who lived in the four areas mentioned, to convey the message that there was no point from which Yisrael would safely be able to attack them without suffering defeat.
Why did the Spies initially convey their message by way of a hint? Why did they not say it outright?
Ramban: Because they were afraid of Moshe and Aharon.
And why did they omit the answer to the question "ha'Me'at hu Im Rav" and "ha'Tovah hi Im Ra'ah"?
Ramban: Because they planned to say outright to the people "Eretz Ocheles Yoshvehah!", indicating that the people were few but exceptionally strong.