By the same plane do you mean the exact plane, like the registration number? or the same type like EMB145? Most of the time the company tries to keep you in the same plane all the day, but sometime you do have to switch, which makes for a hassle, b.c you have to gather all your gear and do all the setup checks all again.
At my company we fly three types of the EMB 145/140/135. It is possible to fly a 145 one leg an 135 the next.