Given that chances remain much better that neither will invade, chances are good that "we will see" is a bit off.
With that said, Belarus is the one of the two that Ukraine has been pointedly forced to defend against, that Russia has pointedly been trying to get to invade by fair means and foul, and which has been offering aid and comfort to the forces that are actively invading Ukraine.
Poland, on the other hand, has been actively aiding Ukraine and working to support Ukraine's decision to defend themselves.
Which one is objectively more likely to invade should be about as clear as night and day.