I'm not exactly sure but I think you can fit anything between 275/50-20 to 305/40-20. I'm planning to fit bigger tires to my KMC wheels. I might get second opinion about the tire size. By the way, your truck looks great. What running boards are those?
I've seen those Mickey Thompson Baja Boss tires at 4WheelOnline. It looks like a pretty solid choice for a tire. The puncture resistance and improve steering response are good enough reason for me to get it if I do extreme off-road driving.
I haven't tried installing Bushwacker fender flares yet but I'm considering it as an option for aftermarket fender flares.
Though, I guess you still have to wait for new fender flares that will fit your 2021 Canyon.