According to the profile (which can be found at www.johnmccain.com//About/McCainChildren.htm), Sidney is in the music business and recently served as the General Manager of V2 Records, Canada. Apparently, she loves baseball and makes an annual trip south to the training camps of the New York Yankees and the Toronto Blue Jays.
Out of curiosity, I plugged Sidney McCain's name into my favorite search engine. I found a very interesting article about her in the February 2006 issue of Toronto Life recounting her search for a place to live with her boyfriend (check it out at www.torontolife.com/features/the-new-starter-home/?pageno=4). I found the article interesting on a couple of counts. First, there's no mention of Sidney's famous father. Second, a picture of Sidney is included. Here it is:
Wow, Sidney totally looks like her dad! And, wow, her boyfriend totally looks like a dough-boy loser! Can you picture THAT guy at official dinners at the White House? Disturbing.