If you want to download Mass Effect 3 and get the most for your money, you'll have to turn to EA's Origin service instead of Steam.
According to the game's page on Origin, it's the only place you'll get the PC Digital Deluxe Download of Mass Effect 3. This is a change from Mass Effect 2, which offered the deluxe edition through other download services.
Gamers who prefer buying boxed copies don't need to get alarmed; the bonus content in the downloadable deluxe edition is basically the same as the retail Collector's Edition. In fact, the retail package has some better bonus goodies (like a 70-page art book and a fabric patch) for the same price of $79.99.
Are you going to download the game instead of buying the retail collector's edition on PC?