It though to answer precisely to your answer without knowing about your educational background...so here is my best shot...
1) If you are from CEGEP you need to do the full civil law LLB program of 3 years at UdeM and after completion you may do a one year JD (Juris Doctor = Common Law) program (32 credits) that makes you eligible to write the bar in the state of New York or other Canadian provinces. Nowadays, most civil law schools have either the option of doing a one-year program after your LLB in a Common Law school in Canada to get a JD or some such as UdeM or Sherbrooke offer it on their respective campuses.
2) If you come with a completed undergraduate university degree you may do at UdeM kind of a fast track combined program where you can obtain both an LLB & JD in three years. Basically you do all your core credits in the two first years and then your last year is 100% Common Law classes in English at UdeM. Obviously, this program seems to be more intensive and forces you to take summer classes if you wish to complete everything is 3 years.
You can find more info here: http://droit.umontreal.ca/fileadmin/droit/documents/PDF/programmes_combines/LLB_JD_etudessuperieures.pdf
There is also other criteria that UdeM takes into consideration, however this is a summery from my own understanding.
However to answer your question, I cannot say per say depending on what you applied, yet I guess you applied to the civil LLB program. You need already to be into law school (2nd year) to apply to the Common Law JD program with a min of 2.7/4.3 to get in if you have a previous degree. If not once you graduate law school (LLB) you can do the one year program separately offered both full and part-time.