Originally Posted by stifle

To be precise, you need to get non-EU passport checked and your online boarding pass stamped at the landside check-in desk, and the gate agent will again check that it matches you and your boarding pass.

Additionally, the boarding pass instructions state that it must be printed on A4 paper. North American paper is not A4. No idea how strict they are on this, but I would try to avoid putting myself in a position where Ryanair could claim I had failed to comply with its absurd rules.