Tomorrow we'll probably encounter the enemy forces.
Literal
Tomorrow we [topic-は] enemy-army [to-に] run-into [probably-だろう].
出くわす is a vivid compound verb meaning 'to run into, to come across unexpectedly.' 敵軍 ('enemy army') is military vocabulary. 我々 is a formal first-person plural, more elevated than 私たち. ~だろう adds speculation.