Various theories . . .
We would be contacted, sort of invited to join with them, like a United Planets.
We would be contacted, sort of indicted for crimes of which we might have no knowledge or understanding.
We might bump into each other, in our clumsy first meandering into the vast sea of space.
We might eventually discover that we are the only intelligence in the Universe to have developed a space program.
We might be attacked.
We might be snubbed.
We might find new friends.
We might find new enemies.
I'm pretty sure we will not find them to be at all humanoid.