In A Storm of Swords, on their way north, Meera begins to tell the story of the Knight of the Laughing Tree. That story is interjected with a side story about Howland Reed's visit to the Isle of Faces:

"No one visits the Isle of Faces," objected Bran. "That's where the green men live."

Bran closed his eyes to try and see the man in his little skin boat. In his head, the crannogman looked like Jojen, only older and stronger and dressed like Meera.

"He passed beneath the Twins by night so the Freys would not attack him, and when he reached the Trident he climbed from the river and put his boat on his head and began to walk. It took him many a day, but finally he reached the Gods Eye, threw his boat in the lake, and paddled out to the Isle of Faces."

"Did he meet the green men?"

"Yes," said Meera, "but that's another story, and not for me to tell. My prince asked for knights." -ASOS, Bran I

Meera then resumes the story of the Tourney at Harrenhal and the Knight of the Laughing Tree. In this post, I want to discuss, how Bran is going to end up hearing that story.

Whose job is it to tell Bran about Howland's trip to the Isle of Faces?

Note: Its very possible, if not likely that this is just GRRM being poetic and that I am reading too much into this line.

But, hey I don't have much to post about these days, so I am going to approach this post with the following logic:

• There is going to be a "telling" of this story to Bran
• Meera knows who is going tell it

Options:

We can rule out Meera, as she has stated that "its not her story to tell".

Bloodraven

The Last Greenseer, its very possible that Meera is referring to Bloodraven showing Bran things using the trees.

If interested: Accessible Weirwood/Heart Trees

Howland Reed

The story is about Howland's trip to the Isle of Faces. Its possible that Meera believes that it is his job to tell Bran the story.

If interested: The Weirwood at Greywater Watch and Weird Happenings around the God's Eye

Bran (himself)

Bran could use the trees/beyond the trees on his own without Bloodraven. Its possible similar to his vision of his father and the Winterfell weirwood, he could do the same thing to the trees on the Isle of Faces.

Jojen

Possible since he has green dreams, and has probably heard the story from his father. That said if it was "his story to tell", we probably would have heard it already. Especially if Jojen = paste.

Combination

Its possible that some combination of the above are how Bran experiences the story. For instance while in Bloodraven's cave, Bran could use the weirwood (after possibly eating Jojen Paste) to view the Isle of faces.

TLDR: Bran is going to experience the story of Howland Reed's trip to the Isle of Faces either through the trees with Bloodraven or later in the story from Howland Reed himself.