Rashi on Numbers
חזק הוא ממנו [FOR] THEY ARE STRONGER ממנו — They said this, — if this were at all possible (i.e. if one may be permitted to say so of God) — with reference to the Omnipresent (ממנו, stronger than “He”, they thus uttered blasphemy) (Sotah 35a; Arakhin 15a).
Sforno on Numbers
לא נוכל לעלות, for they will stand up against us and will prevent us from making progress just as happened after the sin when the Torah describes the Amalekites (described as Canaanites) descending and inflicting casualties in 14,45.
Or HaChaim on Numbers
The spies retorted by bad-mouthing the land of Canaan saying that even supposing that the Israelites were able to overcome the local inhabitants, the land was not worth having as it consumed its inhabitants.