What does "Venashal" mean?
Rashi: It is an expression of casting away. 1
Rashbam: It is an expression of breaking something away from its source. 2
Targum Yonasan: It means that Hashem will exile.
Vayikra Rabah (17:6) and the Yerushalmi (Shevi'is 6:1) say that the Girgashi fled and did not fight; the Torah omits them in Shemos 3:8, 23:23. If so, why are they included here? They were not driven out of the land by force!
Malbim: The Torah teaches that many of these nations fled by themselves, just like the [entire] Girgashi nation fled.
Perhaps the Torah did not want to omit them, lest Yisrael fear that we will not defeat them. In Shemos, before Hashem decreed to kill Dor ha'Midbar, and before the Emori defeated the Mapilim, there was no concern for this. The Torah did not explicitly say that they will flee, for that would remove their free choice. 1 (PF)
The Torah is not talking about driving out the nations ny force but about separating them from it (Refer to 7:1:1:1-3) which includes the Girgashi.