Within 1 year, you need to visit Canada along with your family members who will be accompanying you. Please don't miss this deadline. Better try to visit within 8-9 months so that you have enough time in hand.
Your visa will be effective till completion of ONE YEAR from the date of your and your family members medical examination.
Example; If the medical date is 15 MAY 2010 , your visa will be valid only till 14 May 2011, irrespective of the date of stamping the visa on your passport. So it is necessary to land in Canada well before May 2011. Considering the flight availability and any anticipated problems you should plan at least two or three weeks ahead of your visa expiry date which is ONE YEAR COMPLETION OF MEDICAL