To update, I was able to book this:
YYZ- IAD (AC or UA) IAD-AUH (EY) AUH-JNB (EY) JNB-CPT (SA)
CPT-ADD (ET) ADD-YYZ (ET)
I got a very helpful agent who inputted everything one flight at a time starting with the AC flight to IAD. When we were done it came out to 131,356 points and $194.71 in fees and taxes using my last priority reward, I asked if he would sub out the AC flight for a UA one and it went down to 100,000 points, but I now have a 13 hour layover instead of a 4 hour layover,
If room on a better UA flight opens up can I switch or will it reprice? I'm sure it would if it was an AC flight,