I use this one:
It only fits in the CRJ9 overhead bins if not stuffed to the brim. It fits ok in the original dimensions (31 x 43 x 41 cm) but if you pack to much into it... it won't fit.

But as jamesbrownontheroad said, not a problem. They will gate check trolleys for delivery at the aircraft on the CRJ9 and the ATR flights. I usually prefer to go for the delivery at the aircraft option and not have the issue "will it fit, will it not as I packed the power-supply of my Macbook in the wrong spot?" on the CRJs.