I have seen two problems with PokerStars under Crossover:
a) resizing of windows does not work - as noted above, the window resizes, but the PokerStars app seems to not get the message, so it does not re-size the graphics. When the window is made smaller, the image is clipped (instead of shrinking); when the window is made larger, there is a border of garbage (the garbage is clearly derived from the correct graphics, but it's still garbage).
PokerStars itself obviously still thinks that the window is the original size.
b) occasionally, sound will simply stop working. When the sound goes silent, I typically try to toggle the sound off/on in PokerStars. This usually FREEZES PokerStars. The only thing to do next is to kill Crossover and re-start. On re-starting PokerStars, we find that the sound has been successfully turned OFF, and turning it ON now works.