I like it but the effect might even be too powerful for $5 (but not strong enough for $6).
I would suggest doing it this way:
"Discard up to three (or four) cards from your hand. Reveal a card from the top of your deck per card discarded. Discard any of the revealed cards, putting the rest back on your deck."
I think +1 buy, strong sifting, then +3 cards is stronger than cantrip plus strong sifting (Cartographer), because not only can you pretty much choose what cards you draw, but you can draw them in the same action, so I don't think this should look as many cards as Cartographer does so easily, despite the discarding drawback.
Besides, there are other versions of a stronger +3 cards at $5 without the +Buy (Journeyman, Catacombs).