This is a global version of Overwatch: Origins Edition, so you can play in any region
You need to create an account with Argentina set as the country, you can than purchase it from the webstore or from the battle.net laucher
Unfortunately you can not gift the game from this region onto another account e.g. if you played the free weekend
GIFTABLE VERSION -
If you register with a mexico account instead, you will then able to purchase a giftable version for ~ $39.20 AUD which can then be used on an existing account
NOTE
If you have any difficulty paying by card, add the card to your account first
Can you play on Oceania servers?