The answer is no. CGA exam have nothing to do with the CPA exam.
Also, if you are not interested in US tax position or moving to U.S, I suggest you not to waste time and effort to pass the two exams, only CGA is enough.
To yuu:
What courses you already took in McGill and what province are you going to enrol. There are big differences B/W Quebec and other provinces in CGA programs. If you have no confidence to pass French language exams, You must follow the course list of CGA Canada. Otherwise, you will meet problems when you transfer file to other provinces. CGA need not experience when you take exams. Once you apply CGA designation, You need at least one year senior accoutant experience in Canada ( Ontario rule). In Quebec, two year accounting experiences is ok but you must pass French exam. All accounting courses you took in McGIll will be recognized by CGA. You can follow the courses list to finish all level 1-4 courses in McGill then transfer credit to write pace level exams in CGA.