You can apply the renewal before the expiration date or after. If you apply before the expiration date, you can keep the card at the moment and once the new card is issued, you will have to handed in the old card in order to receive your new card. You can still travel abroad with your current card and if your return date is beyond the expiration date of your current maple leaf card, you will need to go to your local canadian counselor asking them to issue you a travel document so you would be able to return to Canada.