What is the nature of the fear that Hashem will cast upon the Cana'anim?
Rashi, Ramban, Rashbam, Targum Onkelos and Targum Yonasan: It consists of a feeling of dread that causes them to become confused.
Sotah, 36a: When Yisrael crossed the Yarden, there was not a soul who could stand up to them, and anyone who attempted to do so, suffered stomach upset, 1 as the Torah writes "Es Eimasi Ashalach Lefanecha ... ".
Oznayim la'Torah: It is answer to Moshe Rabeinu's request 2 "Tipol aleihem Eimasah va'Fachad".
What are the connotations of "ve'Hamosi ... "?
Seforno, Targum Onkelos and Targum Yonasan: It refers to the confusion that results from the terror-stricken feeling. 1
Rashbam: It refers to the thunderous noises that Hashem will bring about that will cause terror among the enemy nations. 2
With the result that they will turn round and flee (as the Pasuk concludes), like we find with the Egyptians, when, by the Yam-Suf, they proclaimed "Let us flee before Yisrael, because Hashem is fighting against Egypt on their behalf (Shemos 14:25 [Seforno]).