If I buy a retail copy of ME2 can I register the game on Steam? 

Add a game... -> Activate a Product on Steam. It says you can enter your retail key or Steam key in order to register the game.

You can only register specific games though.
 
Here is the list: 
https://support.steampowered.com/kb_article.php?ref=7480-WUSF-3601 
 
Hope this helps.

So the answer is no, you cannot register the game on Steam.

EA, Ubisoft games can't be register a part of Steam. plus, what interesting is that Steam doesn't sell any EA, Ubisoft games at all.

" EA, Ubisoft games can't be register a part of Steam. plus, what interesting is that Steam doesn't sell any EA, Ubisoft games at all. "

" EA, Ubisoft games can't be register a part of Steam. plus, what interesting is that Steam doesn't sell any EA, Ubisoft games at all. "