The standard Canon 70-300 USM IS is a very good lens and at a decent price too.
Make sure you get an IS version. Not much extra $$$ and well worth it.
Take a tripod for the landscapes but for safari I recommend a mini beanbag to rest the camera on vehicle door sills or other parts of the vehicle. You may well be going on dusk drives for big animals and you will need a support even with IS but there will be no room for a tripod. A suitable bag is better than a monopod.
Hope this helps.