Couldn't find a clear answer for that online. Most people say it doesn't hit 60fps. Digital Foundry reports that LM2 has an 'unlocked' frame rate, which I'd guess maxes out at 60fps but falls short of because of hardware limitations. It's no better on N3DS, as seems to be the case with titles released before it.
Worth noting that the original Luigi's Mansion was only 30fps. I feel like they wouldn't feel the need to improve on that much for a handheld sequel/remake.
I haven't played the original yet so I'm probably going to get the 3DS version. Liked Dark Moon a lot despite being interrupted by Egad every time I entered a room.