FP will only allow you to book passes at one park at a time - if you plan on doing Epcot and AK in the same day (I wasn't sure based on the way you worded your question but that's what I thought you were asking) - what I would do is plan to Rope Drop Flight of Passage, get a FP for Navi'i river ride and two other rides in AK. Once you've used your third FP, you can then book FP at the park you want to hop to (in your case, Epcot). You can only book one FP at a time after your first 3 for the day, so just be aware of that.