Which breed cat is this? Anyone? He has very chubby cheeks.

>>2121721
That is the Chubby Cheeked Lawn Chair cat

>chubby cheeks

This is the mark of a male cat that either hasn't been neutered or wasn't until he was well into adulthood. Intact males develop hella jowls.

Looks like a standard American tabby to me.

It's a moggie

Just a moggy. Tomcats often have broad skulls and puffy cheeks if they're left intact or fixed late.

Like >>2121795 said
Chubby cheeks are a result of male hormones when the cat is an adult