The Can of Beans is available in the Friendship Shop, a special vendor placed at the peak of the expanded Beanstalk event.

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During the Beanstalk Event in Grow a Garden, at the top of the Beanstalk, there will be an Event Shop where you can buy items ...

Basically in the Beanstalk event, players can grow the beanstalk sprout into a giant plant by giving different plants to it.