Well let's look at the possibilities.

They have 4 games right now that are out, or coming out in Japan that are guaranteed to sell 1 million copies, some maybe even first week.

Fire Emblem Fates, Youkai Watch Busters, Youkai Watch 3, and Animal Crossing Happy Home Designer.
Which brings their total to 42

Anything with the word "Pokemon" on it is guaranteed to sell 1 million minimum.
And I still believe we will get ONE more Pokemon RPG before Nintendo calls it quits with the 3DS, so Pokemon Z or X2/Y2 is easily going to crack it. Which brings the total to 43.

There are some games that haven't cracked 1 million yet, but will get there eventually. These games I believe are Fantasy Life and Sonic Generations. So 45.

Also, just like Pokemon, anything that has the word "Mario" in it will sell 1 million copies. So Mario & Luigi: Paper Jam can be added to the list. 46.

I want to say the same thing for anything with the words "Legend of Zelda", though I have my doubts about Tri Force Heroes. Not in terms of quality, I think it's going to be a damn fine game. But the last Zelda game that had multiplayer didn't fair so well in terms of sales for Legend of Zelda standards... but that game was on the GameCube, and this is the 3DS, which has already more than doubled lifetime GameCube sales... Yeah sure I'll give it the benefit of the doubt. So 47.

But I have even bigger doubts for Bravely Second. Even though the first game managed to crack the 1 million barrier, it came out at a time when the 3DS was at its peak & was considered the king of gaming, now that it's on its way out, I'm not to sure.... But, since the first one was so well received and has an established fan base, along with a higher install base to work with... I'll give it the benefit as well, but I think it'll take some good legs.
So 48.

And that's all I can confidently predict at the moment. Even then it needs 9 more games if all of the above turns out true. Plus, there are still PSP games that are around that barrier and still being tracked, so the number  of PSP million sellers is likely to increase.
We'll just have to wait and see.

DQ VIII will hit 1 million without the West.

OT: I doubt it. As Teeqoz said, the PSP can still minimally increase its collection of million sellers, but I don't think the 3DS has that much steam left in it. After 2016 I doubt there will be any party left in the 3DS.

Well VGC says those titles sell (not much, but enough to get them to a million) and I can believe there are copies of those games in bargain bins around the world, so yes on all accounts.

OH! The PSP didnt have a 10M+ game sold with 80M users. While the 3DS have 3 10M+ game sold with 50M users. INTERESTING........

I doubt it but I don't think the gap would be that far off

-For the record, here are the upcoming 3DS titles I believe will hit 1m for sure:
Fire Emblem Fates, Animal Crossing: Happy Home Designer, Yokai Watch Busters, Dragon Quest VIII, Monster Hunter X, Monster Hunter Stories, The Legend of Zelda: TriForce Heroes, Pokemon Super Mystery Dungeon, Mario & Luigi: Paper Jam and Yokai Watch 3.
-The upcoming games that have potential but I'm not sure:
Bravely Second, Rhythm Heaven: The Best+ and Yokai Sangokushi.
-Current games I think could leg it out to 1m:
Sonic Generations and Fantasy Life

And then of course unannounced games that would make it to 1m like Pokemon X2/Y2 or Super Mario 3D Land 2.
Oh, and apparently Mario Tennis Open is already a million seller (VGC just has it under tracked by quite a bit) so I'll add that to the OP. But what makes this comparison interesting is that nothing is set in stone, and it could go either way very easily.

Yes, of course.

Fire emblem, animal crossing home, Zelda multiplayer, Yokai watch 3, mario+paper mario are all pretty much guaranteed million sellers. I'm not sure if it will reach 56 though because this is probably the last holiday season for the system as the main HH of Nintendo as I believe that the NX will be replacing the 3DS (and also the wiiU if it's indeed a fusion system).

You also have to add Youkai Watch Three Kingdoms, Dragon Quest VIII, Monster Hunter Stories, Monster Hunter X and Hyrule Warriors Legends :)

So there you have 53 :D 

I think it all depends on when the next Nintendo HH is out and when the 3DS is pulled from the shelves. PSP had a bigger install base and has been out for a longer time, so it'll be hard for the 3DS to have more million sellers...