They'll both have online multiplayer but it won't be cross console. So you won't be able to play against someone on a 3DS if you're using the Wii U version.

Well Brawl sold a ton due to Wiis instal base. But Melee on GC only sold 7 million, which is more comparable to what the WiiU would pull in.

Uncharted's last outing was around 6 million, but PS4's install base is climbing higher then PS3's so mathematically it will be a close one.

legit.
i doubt ssb4wiiU will sell more than 5 million

First weeks? Sure.
Life time? Don't know...

I think every single Smash Bros game potentially outsells all the Uncharted games put together

So as weird as it is, based on the Wii U failing so badly, I think it is actually possible that Uncharted PS4 might actually outsell Smash Bros on Wii U.

the way the WiiU is selling, even if 100% of users bought the game, Uncharted 4 may outsell it

There is a good chance it will. Both franchises have increased in popularity over the years (and Smash Bros sure is the biggest of the two at the moment), but the PS4 is selling like crazy and the Wii U is not.

If I'd take a guess, I'd say Smash Bros U will sell ~3 million this year. No idea about Uncharted 4 though.

I'd say the max amount SSB4 will sell is a little above 7 Million. That's around how much SSBM sold when it was still a newer game series, as well as being on an extremely impoverished console, sales-wise.

Uncharted could decline in sales a little, but also do around the same or a little more. It's a close call.

Add in 3DS? Uncharted has no chance.

This is a joke right?

Why do you say that? It's pretty likely that they'll pull similar numbers.