"우리는 케이크를 먹을 것이에요."
Translation:We will eat cake.
Not exactly the same meaning.
going to infers a future plan that is not completely decided. Whereas
will infers a plan that is set in place and fully decided. However, we do often use both interchangeably.
i think going to is a better translation to english. Will is rather strong and often used with 'threats' whereas going to is future plans and predictions
I think using "will" to mean "(to be) going to" sounds natural if contracted. e.g We'll eat cake.