This one's hard to predict, because I think it can go in all directions.
Will it blow up and have the 'New Super Mario Bros.-effect' because of the game's retro style, or will it suffer the 'second Zelda curse' selling below Ocarina of Time 3D merely because it's the second game on the system?
History shows that's the likely course of action, because that's what always happened. Whether it be home-consoles or handhelds, the second Zelda game always sells less than the first.
Usually, that first game is an original game though so that should give A Link Between Worlds an edge. However, the existence of the GBA A Link to the Past remake which came before Minish Cap and outsold it puts a damper on this rule. Okay, A Link to the Past actually did came with an original game; Four Swords, but I highly doubt that was the reason for it selling. And okay, Minish Cap is a mediocre game not actually made by the Zelda team.
Then there's case of Phantom Hourglass. The DS games follow all the rules; the first sold more than the second. Phantom Hourglass sold 5m copies and is thus the best selling portable Zelda game. The game however isn't very liked among the Zelda community and in the entire gaming world. Something A Link Between Worlds does seem to be. The game has a good amount of hype going on and userbase is largely irrelevant when it comes to Zelda games.
I think the hype and the retro-feel will negate the 'second Zelda curse' somewhat, but the game's sales won't blow up either because of it. I don't think it will beat Phantom Hourglass, but will break the rules and sell more than Ocarina's remake.
My prediction is 4.6m
