The biggest cost of car ownership is depreciation. I don't know what kind of resale an Infiniti will have after a number of years, but BMWs have proven to retain their value much better than most cars. Would probably be a good idea to check resale values on the two brands by looking at classified ads. For example, if you expect to own a car 4 years look at ads of cars four years old and compare that with the MSRP of that car when it was new.
Also, does BMW Canada pay for maintenance? In the US they pay for everything but the tires for four years and 50,000 miles and it sounds like the program in South Africa is even better.