Can anyone tell me if the "Hankook Ventus RH05 325/50R20 will fit my truck without modification?

They also make the same tire in 295/50R20.

I currently have the stock Goodyear P275/60R20s.

Additionally I noticed BF Goodrich has a 285/55/20 but its only available in Canada, Why?

Thanks

The normal 20" sizes for the standard cab model would be either 275/60-20 or 305/45-20 depending on the wheel. We have never test fit a 325/50-20 You'd have to check with a Hankook dealer for test fit information on that size. None of the tire companies we work with even make a tire in that size.