Brutus and Cassius die in rather simliar ways, but Caesar's death is very different. What is the meaning of this contrast?
This is a very good question, as one would imagine that Shakespeare is making a point about the characters through how they die. This could be possible, and I'll look at the different deaths thematically in a moment, but first, it is important to note that this play is based upon historical fact and is accurately reporting the method of death for each real life character. So, whether, hisotrically speaking, Fate directed their deaths and provided "meaning" in the "contrast," is not something we can know.
In the play, however, honorable action is a key theme. This theme plays into the different deaths in that both Brutus and Cassius take their own lives (with assistance), while Caesar is set upon and murdered. Brutus and Cassius decide to end their lives, as they see this as the most honorable course of action left to them. Caesar is killed because others believe that he is acting dishonorably, even though he, Caesar, sees himself as completely honorable.
So, while the deaths are required by historical fact, we can still find some meaning in contrasting the deaths of the of Cassius, Brutus and Caesar in relation to the theme of honor.