The porch floor slopes from the house floor from about 7/8" to 1-3/4" and I plan to install engineered wood flooring over the entire room. I have tried a plywood/sleeper approach and it isn't flat enough or sound enough. I am thinking an over pour of some type of cement with fiber would be the best solution.

Porches are sloped downward for rain runoff. Is it now enclosed?
What do you mean exactly by 'entire room?'
What is under the porch that protects it from below?
You can't treat a porch like part of the house without all the details from the ground up, including piers and posts.