Upvote:5
Vancouver-Montreal is a domestic flight. Thus, you will pass immigration as you arrive in Vancouver, after which you are inside Canada. You can then move within Canada however you want, you can even ditch your plane ticket and decide to walk to Montreal (not recommended).
As you don't want to live in fear of missing the connection, I suggest you meet your sister in the landside (publicly accessible) part of the airport. Remember to make sure you have enough free space in your hand luggage for all the winter clothes, as your bags are likely to be checked through from Manila.