Do yourself a favor and stay away from the EF 75-300 mm f/4-5.6 III. Of all lenses in Canon's current line-up, it competes well to win the title of the lemon of them all.
To get something similar, but much better, look instead at the EF-S 55-250 mm f/4-5.6 IS STM. You'll be much happier with that one. If you absolutely want something which in the future will mount on 24*36 mm sensor cameras as well, then look at the EF 70-300 mm f/4-5.6 IS USM. But leave the 75-300 behind!