England captain Dylan Hartley has been ruled out of the tour due to concussion, and the Sarries fly-half is among the favourites to replace the 32-year-old as skipper.
Farrell has won 58 caps for England and captained the XV during their Six Nations defeat by France in March when Hartley was sidelined with a calf injury.
"It's up to England whether Owen goes but I'm certain he will go. I haven't heard anything to the contrary and I'm sure he wants to go as well," McCall told Sky Sports News.
"He would be a brilliant captain. He is ready to do that job and has the respect of everybody.
"He has a fantastic rugby mind but he is also brilliant at getting the best out of his teammates. Both of those things combined make him an ideal captain."
England coach Eddie Jones is expected to name his squad for the South Africa tour next month, the three-Test series beginning on June 9 in Johannesburg.