If you are going with the Wild 4 crew, you will have a blast. Stu, Justyna, Ann, and John are great folks.
Stu has a couple of Canon 500s, Wimbley gimbles, and tripods to rent. We rented a set each. We used the 500s throughout the trip. We used the tripods and gimbles at a private lodge to shoot crocs abd birds around their ponds. If a set is a available, you might consider renting them during the trip.
Without doubt I used the 100-400 with the 7Ds the most because so many times the Kruger animals are within 15-40 meters from the vehicle. The few times I remember using the 500 in the truck in Kruger was to shoot a leopard in a distant tree or wading birds in the a far bend of the Sweni river. So if you have your 70-200 on the 5D and your 300 and converter on a crop body, you should be ready for almost anything. Since Stu shoots Canon, he can provide extra advice on what to bring. But have a good walkaround lens like 24-105 for the 5D for those times when you are shooting people, and VERY close animal shoots...not to mention the great people.
Take lots of large fast memory cards. We were shooting at least 4 16GB cards each per day ( 64GB each per day to download). So you want a fast way to download the cards at night. Use a card reader hooked up via FW800 or eSATA or USB3...definitely not via USB2 or FW 400. We had not had our 7Ds but a few days before going on the trip. We were not used to shooting video and did not shoot any. Big mistake. So next year we will be additionaly shoot video. So that means needing even larger/faster cards. The good news there is that fast 32GB cards are becoming relatively inexpensive. Compared to the cost of the safari...a stack of large fast cards and a fast reader is insignificant.