My friend, currently goes to seneca, and he wants to apply to McMaster faculty of business.

How should this be done? Is there any admission assistant for the faculty business?

I think that he should apply to mac through ouac 105D :
http://www.ouac.on.ca/ouac-105/

If he's an international student, i think he should use ouac 105F. Someone who's in business can answer your last question. I think your friend should talk to an academic adviser/counsellor about the whole procedure, would help him a lot.

all has to be done through ouac. make sure he fills out the right application (105D) unless he's international which then it must be 105F as jim1 said