Who is Moshe speaking to?
Rashi: He is speaking to the tribes of Reuven and Gad 1 mentioned earlier, who will lead the troops into battle on account of their immense strength. 2
Targum Yonason: He is speaking to the tribes of Reuven and Gad and half of Menasheh. 3
See Na'ar Yonasan.
Refer to Devarim, 33:202:1 & 2 and 33:20:3:1. (This does not follow the Gemara in Megilah 16a, which - based on the Pesukm in Vay'chi Bereishis, 49:8 and Tehilim 80:3 - implies that Yehudah, Binyamin and Efrayim are the strongest tribes,. Perhaps only in the generation that entered Eretz Yisrael, Gad and Reuven were strong (PF). Refer also to Bereishis 47:2:151* & 47:2:151:1.
See Yehoshua 1, 12-16.
Why did Moshe say "Kol B'nei Chayal" and not "Kol Yotz'ei Tzava mi'Ben Esrim ... "?
Oznayim la'Torah: Refer to Bamidbar, 32:21:2:1.