So far, Capcom has not commented on whether or not online play for MH3 will be free. The japanese version isn't, but the game's predecessors were, for NA players.

Now gamespot has confirmed that the preorder-bonus for the NA release of Monster Hunter Tri is a 500 Wii points card. 
On the one hand, DLC for this game is confirmed so this might just mean that NA preorders get this content for free, and they're too lazy to put it on the disc. On the other hand, this could be a strong indicator that they are confident enough in this game to charge NA players for online play... a move that I don't see succeeding in any way.

Charging for it over here does seem like an error, I would say the DLC is much more likely.

It doesn't equal confirmed...but it's a big indication.

The free 500 Wii Points Card are for whatever you want to be. It's a freebie.
 
Monster Hunter 3 is free to play.

" The free 500 Wii Points Card are for whatever you want to be. It's a freebie.  Monster Hunter 3 is free to play. "

If they do the same for Europe, then it's a buy, could probably convince a friend to get it to. If not, forget about it!

It was all clear in the press release, free play and 500 points bonus, no reason to revive threads that were wondering prior to the official announcement.

@RockmanBionics said:

" If they do the same for Europe, then it's a buy, could probably convince a friend to get it to. If not, forget about it! "

Yeah it's free to play, and charging for it would be the biggest mistake Capcom would make. This game has no footing outside of Japan, they need all the help they can get.