Labo is just the more interesting bet.

GoW sells gangbusters, that's all part of the plan. Nintendo moves cardboard like hot cakes and everybody loses their minds.

That could still mean it doubles the sales of God of War.

What? No, no, no, no. That is unlikely. I assume GOW can sell more than it's predecessors, but growing THAT much seems extremely unlikely.

Well, a bit difficult to answer. I think this GOW can be the best-selling in the series, say 6M. But Labo has more potential. People seem to forget, that it already has two SKUs: Toy-Con 01 (Variety kit) and Toy-Con 02 (Robot kit). The numbers imply Nintendo has planned more and the trailer shows stuff that isn't in either of the two kits. So we can expect Nintendo will release the next two kits at the moment the hype starts to go down on Labo. I expect at least 4 SKUs of Labo, beating GOW would mean they each need to sell 1.5M. Clearly doable.

God of war will win early on. Labo will pass God of War later because it is multiple products.

I think this God of War will probably do 8 million lifetime.

GoW will sell 10m at max.
Labo has not real sales ceiling.

GoW is one item, that appeals to a select group of people.
Labo is many different objects that can be purchased; some Labo may capture different audiences.

Wow, what a random pair to compare. Well, they have the launch date in common.
I think Labo will easily sell more, because it's more than a single game. It's a whole system of.. something. And a significant portion of Nintendo fans will take up anything they come up with as a matter of principle. Hard to predict what kind of longevity the Labo will have though.

you underestimate the ability of nintendo's capacity to sell absolute nonsense to its fans. 

Is God of War really well known outside of the gaming sphere? I know each game sells millions, but I never see it referenced or see merchandise for it like I have for a lot of other series like Mario, Sonic, Final Fantasy and even Crash Bandicoot

That said, I still think it'll outsell Labo, lol, but I could end up wrong and eat delicious cardboard crow.