Slamdown Town / Maxwell Nicoll and Matthew Smith.

Enhanced descriptions from Syndetics:

A boy's wish to be a star wrestler is granted in this wacky middle-grade fantasy Ollie and his older brother, Hollis, have wrestling in their blood: Their mom was a pro whose dreams of stardom were dashed by a devious opponent. Now she's an overworked, underpaid ref at Smackdown Town, the local arena. Ollie's goal in life is to win the golden championship belt for his mom-immediately followed by his other goal: to hang his bully of a brother from the roof by his tightie-whities. But there's one problem: Ollie inherited their estranged dad's puny frame, while Hollis got their mom's brawn. Thus Ollie has resigned himself to a fate of wrestling mediocrity and wet willies . . . until the day Hollis gifts him a piece of stale gum and forces him to chew it. Ollie soon discovers that the gum-bought on eBay and formerly chewed by a wrestling legend- has an unusual side effect: the ability to physically transform Ollie into a pro wrestler. As Big Chew, Ollie's finally able to put Hollis in his place and be a star. But when trouble befalls his family, being Big Chew gets a lot more complicated. In the end, Ollie knows he can't have it all; and it's only when he asks himself who he really is that he learns what it means to be a champion.