set cubase to send mtc and mmc under Sync -> Setup. Set cubase to 30fps (you can do this on the transport bar for sure)
on the mpc go to midi/sync page (shift 9 i think) set it to receive mtc 30fps and receice mmc.
now when you hit play or rec/play on the mpc it will 'standby' until it receives a start message from cubase. simply hit start (or stop, whatever) in cubase and both will start at the same time. be sure to set the same tempo on the mpc and in cubase.