I just googled it. According to Edge magazine, Tri-G will be coming out in Europe and the US later this year. That was in February. In April, Chris Svensson of Capcom USA was asked if the game was not coming out in the US and he said, "Have we said that? I think it's fair to say I've said everything that I can on this topic without getting myself in trouble. Please be patient." that sounds like the game is being brought over but I suppose, we'll see.
I thought the Edge report was formally denied as rumor (which doesn't mean it's false), but could be wrong and don't care enough to check. Regardless, no official announcement has been made by Capcom and there certainly is no official release date or window known for Monster Hunter in North America. I fully expect it to come across eventually because Capcom never met a port it didn't like, but have no intention of holding my breath until it gets here.
Oddly, even knowing if/when the Monster Hunter games are coming would only serve as further disincentive for buying a 3DS XL since it doesn't include the extra circle pad that is highly recommended for playing. Other games like Resident Evil and Metal Gear Solid will also be affected by this design decision.
I'm probably in the minority, but I can't see why Nintendo would release this revision without building in the accessory - especially in Japan where Monster Hunter is
the handheld system seller.