U-Haul will have a surge brake. If you want electric brakes, you have to buy a brake controller and install it, or have it installed by the trailer store.

I've never heard of a Bluetooth brake system, but there's no reason it could not exist. Back in the olden days, you would install a 7-pin connector and hardwire the brake system through it. You get 4 pins for lights, and 3 pins for the brakes, or maybe 2 for the brakes and 1 is unused. Whatever. The point is that electric brakes on a trailer used to be connected through the 7-pin connector.