If by aliens you mean extraterrestrial life, then they're likely to exist. Anyway, they would be so different that it would be hard to compare them to us.
Oh, I certainly believe they would exist, even if just some sort of bacterial organism, but some people are convinced that they would be just much more intelligent and advanced than us, which may or may not be the case. It's possible, but not completely likely.
Then it must be a square apple pie, not a circular one. Anyway, I'm a big fan of apple pie, cottage pie, blackberry pie and pretty much any pie I can think of.