the validation period for the visa is commonly based either before the expiration date of your medicals (from the day you undergo medical exams) or your PCC ( from your native land). As i've said that is the common practice in the DIAC, but doesnt necessarily mean that they will always follow that, just for example in my case: meds: may 28, 2012 , pcc: may 25, 2012,initial enty : feb. 2, 2013-initial entry date is almost 4months ahead than the expiration of my meds and pcc.. So in my opinion it is still on the discretion of the CO.