Russia: a verbal aspect question?

In this particular case both phrases are correct and convey the same meaning. As a native Russian speaker I can easily use both phrases interchangeably. However these two verbal forms have a slight difference (which is not important in this situation). When "встаёшь" implies indefinite regularly repeated action (what is not important here as you already defined the tense by saying "tomorrow") "встанешь" refers to a singular action in the future.