Did it hurt when you fell from heaven cause got nice cans - help i get this joke?

This is a pick-up line. It uses a pun and word play. The first part, "Did it hurt when you fell from heaven?" is a common pick-up line that suggests the person being addressed is beautiful or angelic. The second part, "cause got nice cans," is a pun on the word "cans." The word "cans" can refer to containers made of metal, but it is also slang for a woman's breasts. So, the pick-up line is playfully suggesting that the person being addressed is not only beautiful, but also has nice breasts.