MULTIPLE RWY AND DEP CLRNC CHANGES CAUSE CONCERN AT YYZ; ON.

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THE WHOLE CREW WAS ON A CONTINUOUS DUTY OVERNIGHT. WE ALL HAD ONLY 5 HRS OF REST. WE ARRIVED AT THE ACFT AT XA00. WE GOT OUR CLRNC WHICH WAS THE TORONTO 3 DEP OFF RWY 33R. WE PUSHED BACK FROM THE GATE AT XA30. WE CALLED APCH CTL FOR TAXI. THEY GAVE INSTRUCTIONS TO TAXI AND HOLD SHORT OF TXWY AG; THEN CONTACT GND. WE CALLED GND SHORT OF TXWY AG AND THEY GAVE A NEW RWY AND A NEW SID. IT WAS NOW GOING TO BE RWY 23 AND THE BOWLES 1 DEP. OUR TAXI INSTRUCTIONS WERE TXWY A AND HOLD SHORT OF TXWY H. MY FO DID THE TAXI CHKLIST. AFTER COMPLETION OF THE TAXI CHKLIST; I HAD HIM PULL OUT THE BOWLES 1 DEP. WE BOTH HAD REVIEWED IT AND CHANGED THE RWY AND SID IN THE FMS. WHEN WE WERE SHORT OF TXWY H; GND TOLD US TO TAXI TO TXWY H TO RWY 23. AS WE MADE OUR TURN TO TXWY H; GND TOLD US TO CONTACT TWR. TWR SAID 'CHANGE YOUR DEP TO THE LESTER 2.' AGAIN; I HAD MY FO GET IT OUT AND WE BOTH REVIEWED IT. TWR SAID TAXI INTO POS AND WAIT ON RWY 23. WE ARE STILL ABOUT 500 FT FROM THE HOLD SHORT LINE STILL WORKING ON THE CHANGES IN OUR DEP. ONCE THE FMS WAS AGAIN CHANGED AND WE BOTH AGREED OF THE CHANGES; TWR SAID 'ARE YOU GUYS GOING TO TXWY Q?' AND I SAID 'SAY AGAIN.' TWR SAID 'ARE YOU GUYS GOING TO TAKE TXWY Q?' WE BOTH LOOKED AT EACH OTHER AND I SAID 'HE SAID TO TAXI INTO POS AND WAIT; RIGHT?' MY FO SAID YES. THEN TWR CLRED US FOR TKOF. AFTER LOOKING AT THE ARPT DIAGRAM; TXWY H TURNS INTO TXWY Q. TXWY Q TAKES YOU TO THE END OF RWY 23; WHICH IS WHAT OUR CLRNC WAS. GND WANTED US TO DEPART RWY 23 FROM INTXN H; BUT DIDN'T SAY THIS IN HIS TAXI INSTRUCTIONS. THERE WERE WAY TOO MANY RWY AND SID CHANGES. YYZ CTLRS DO THIS ALL THE TIME. THIS NEEDS TO STOP!