good morning, I have questions, i'm using EZDrummer, when I open the piano roll I see all the hit's (notes) for every drum being played. what I notice is that the rectangle's are different sizes, why is that? also when I want to add a note i.e. crash cymbal I look for it on the keyboard pane then insert it. my question is I can't seem to get it as loud as I want even when I increase the velocity to 127. is there any way I can make it as loud as the rest??
thank you, I await your answers.  

How do you mean different sizes? You mean the length of the notes? That quite literally determines how long the note is held for (1/4 note, 1/2 note, whole note, etc). With drum samples you won't really notice a difference. If you had a synth patch loaded then you will.
 
As far as the volume of your crash check the mixer in EZ drummer. You should be able to turn it up there (or turn the other notes down). If you have all the kit pieces sent out to their own tracks in Sonar (recommended) you can also turn things up/down in the Console view just like you would any other track. Velocity does not necessarily equal volume. Especially with drums. The lower velocities of say a snare hit will be like the drummer hitting the drum lighter and the higher ones would be like harder hits so the actual sound may be different. So that means if you have a snare hit that's low velocity like a little tap you could still crank it up to be louder than everything else and vice versa. It is not always desirable to have notes at full velocity even if you want them loud. Also if you intend to put in some nuances if you have everything at full velocity you can only go downward.