In my opinion, 5 1/2 hours is not enough time. Why don't you simply find a restaurant in the airport and eat there. Or a lounge.
I do remember having a friend see me off at the Toronto airport. We weren't able to find any restaurants, so we just had a snack and were off. I wasn't planning to have him join me, but he'd never been in a limo and he wanted to make sure I got off okay.
Are you worried about being bored for 5 hours? I'd rather be bored than get caught in traffic in a friend's car or take far too long to eat.
If you want to eat at the Keg, it's just a chain steakhouse. Same with Moxies. I have only had a few memorable meals in Toronto, probably because, living in small town Alberta, I am only a few minutes drive from really good independent restaurants. If you are absolutely determined to eat at the Keg, I prefer the one on Bay Street. Bar is packed at 515, but the restaurant is nearly empty.
Chuck