There's bold and then there's silly. In order for this to even stand the tiniest chance of happening, there would need to be a major new Mario platformer coming this year to Switch that steals Odyssey's sales thunder and BOTW would need to be the only Zelda game released on the console for the entirety of its lifespan. And even then it wouldn't happen.

As much as I would love for that to happen, it's not going to.

And it won't be a case where 1 is just barely above the other by a little less than a million. It's not going to be even remotely close.
The absolute best case scenario for Breath of the Wild would be 17 million, and that's counting the Wii U version.
Super Mario Odyssey is the Mario game everyone has wanted since Galaxy 2 and it is selling exponentially higher than any other 3D Mario game to date, with more just as much, if not more, critical acclaim behind it.

For comparisons sake,
VGC has Odyssey at pretty much 8 million after 11 weeks.
Within that same timeframe, Galaxy 1 was at 4.6 million and 3D Land was at 4.9 million.
Now, 3D Land is at 11.19 million, and Galaxy 1 is at 11.39 million.
So, those games were around 40-44% of its lifetime sales within its first 11 weeks.
If Odyssey follows that same trajectory, that puts it at a little over 19 million. That would make it the best selling Mario game BY FAR, and even beat some of the 2D Mario games, including Mario 3!!!
Breath of the Wild definitely brought the Zelda series to a level of popularity it has never seen before, but not "Mario 3" levels of popularity.

Also, the idea that 3D Mario has never been popular in Japan is completely asinine. Galaxy 1, 64, 64 DS (a remake), and 3D Land, have all broken 1 million in Japan, 3D Land has even broken 2 million. And guess which game is currently outpacing 3D Land in Japan when you align the launches. Media Create already has Odyssey at 1.63 million in Japan: https://gematsu.com/2018/03/media-create-sales-2-26-18-3-4-18
Additionally, Nintendo's own Financial Data had 1.76 million units in Japan, shipped+digital, by the end of December.
https://www.nintendo.co.jp/ir/pdf/2018/180131_3e.pdf.
So, the theory that 3D Mario is not popular in Japan is complete and utter horseshit. It is not true, at all, unless your definition of "Not Popular in Japan" is a something that is not named "Animal Crossing", "Pokemon", "Dragon Quest", "Monster Hunter", "Splatoon", or "Mario Kart".

Yes, Breath of the Wild is selling incredible numbers. It has set a whole new standard of the Zelda franchise and raised it to a completely different level of popularity, the highest it has ever been... But it's still no match for Mario. Odyssey wins.

Botw is big, like 3d mario big.
But the fact is,that oddesey is selling like the lesser 2d mario games. Both games got a huge bump this gen, meaning that botw can't beat oddesey.

You're wrong. Zelda has a lot of things going against it which Mario doesn't. As you said it was never bundled so it wont get free 5m sales or whatever Mario already gotten. Its on Wii U meaning if you have a Wii U and now own a switchs you might not even pick it up for switch but you definitely getting Mario. Now because its a Wii U game it unfortunately is available for PC as well which should hurt sales additionally (PC version of BOTW is the best version of the game hands down). This and the fact that Mario Odyssey has already outsold it and it came out 7 months after i don't see how Zelda will ever catch up.

Yeah sorry OP but you are just plain wrong. Mario has already blown by Zelda after just a couple months of sales and by a year from now it'll be several million ahead of Zelda. Mario is just a more mainstream franchise, period.

No !

It has absolutely no chance in beating Odyssey,

Both games are going to sell amazingly huge amounts but i don't see how BOTW could beat Odyssey. Both amazing games btw but i see the ceiling for BOTW at about 12m (Switch only) absolute maximum. As for Odyssey, well it's almost a case of the sky's the limit. 20m is entirely possible! That's not to say that personally, i don't  feel BOTW is the better game though.

 Bold? makes no sense

I believe Breath of the Wild will sell 1 million, eclipsing Odyssey’s count. The Switch will return to Nintendo’s glory days, we can expect to see games surpassing 1 million copies.