Lambdu Dai replied to Harikancha, that once you get PR, you must enter Canada by the expiry date quoted in the landing Visa. That's a Wrong info. You can defer your Canada entering easily. The first landing visa will be invalid... but you can always request to issue another visa (this should be done earlier than your expiry date of first visa). Then they will ask you to do medical again. your medical check up is valid only for one year. That's why you will have to do again if you are planning to enter Canada later.