In the piano roll, you can hold shift to give notes an equal end, or shift+option to create equal length.
In the arrange, you have to click first, hold and press shift to do equal length (if you press shift first it deselects whatever you click on). The problem occurs when you try to incorporate the option key... option by itself instigates a stretch function in the arrange, and unfortunately this carries over to holding the shift key - although the regions do make themselves the same length.
You can, however, open up the event list and hold shift+option to make them the same length. Once done, you could then go back and tune 'er up graphically in the arrange. Oddly enough, the shift only (same ending point) doesn't work in the event list.
The behavior is the same for both audio and midi regions. If you wish to edit midi regions in the event list you will have to go up one level. When you select a midi region the event list shows notes & such, so you have to click the 'up level' arrow thing in the upper left corner of the list.