May I pick-up the discard pile if the top card is the same in as the ones in my already-completed canasta. (i.e. it has the needed seven (7) cards)
Yes. Here are a few sources to confirm this.
- Hoyle gaming says "you can pick up the discard pile if you can use the upcard in an existing meld or in a new meld" and that a "canasta is a meld."
- Bicycle cards says "...a player may take [the discard pile]: ... by adding the top card to a meld he already has on the table. Having taken and melded the top discard as described, the player takes the rest of the pile into his hand...." and that a canasta is a "meld comprising seven or more cards."
- Pagat says "In order to [pick up the discard pile], you must be able to meld the top discard, without needing any of the other cards in the discard pile to make your meld valid."
Note: Wikipedia has been updated since the original post, so the below is currently incorrect.
I did find that Wikipedia contradicted this, claiming a player "may only pick up the discard pile if they can use the top card by making a new meld along with two other cards from their hand," but this is the only source where this appears to be written.