I read that in old folklore, the German’s had a Goddess of Springtime and she always had a pet rabbit with her, when she would appear in the spring.  Since Easter is always in the spring, the too events, Jesus rising to heaven, and the occurrence of spring time, just blended into this holiday.  Others say that rabbits are a sign of fertility, which is directly related to the spring season when all things are renewed.  They also say that Easter was originally a pagan holiday that celebrated the rebirth of all things which bloomed and grew; because people made their living and feed their families from the seeds that they planted in the earth.  When Christianity evolved, and Christ was hung on the cross, his resurrection happened during the season of spring, when procreation was celebrated.  Rabbits are very good at procreation, and this is a reasonable conclusion as to why we have bunnies in the Easter scenario.