Guinness isn't like other beers. There really isn't anything else on the market that tastes like it.
In my opinion, it's one of the best beers in the world. The other really great beers are the Oktoberfest beers served only in Munich during the time of Oktoberfest. Those would be a good first beer. Nothing quite like a mug at the Houfbrau House in Munich, German's don't f around with pints, they do liters.
I disagree with Irishlad that American bar tenders can't pour a proper pint. Sure there are some who don't get it, but they are the minority. 90+% of American bars I would order a pint of Guinness in know how to pour it properly.
I grew up many years ago when the only beers in America were domestic, I never really liked any of them until one day I was riding in a truck with my Dad on a hot summer day, no A/C, windows rolled down on a very dusty road in Colorado. I was parched. The only thing we had to drink was some Coors beer that was on ice in a cooler in the back of the truck. I was maybe 12-14 yo. I downed one of those cans in like two pulls. I've loved beer ever since. For the record, I hate Coors, Bud, Miller, PBR etc..
Point being, beer regardless of which one you drink first is an acquired taste. For people who like beer, Guinness is often an acquired taste - but one worth acquiring. I never liked Guinness myself until I went to England and had it there. Been hooked ever since. Guinness in Ireland is only marginally better than what is served in the US bars, Guinness Genuine Draft in a can is about 80% as good as what comes out of tap. In Ireland, the only place I had a noticeably better pint of Guinness was at the Guinness Storehouse in Dublin, and that was just because I think it tasted fresher. All beer is better when it's fresh. Beer does not age well. So, if you go to a bar that serves Guinness and you don't see other people drinking it - odds are pretty good their supply of Guinness won't be the freshest. Therefore, best not to pick a Guinness. In Ireland, 80% of the people in every pub is drinking Guinness - therefore it's always as fresh as it can be.
No other stout style beer comes close to matching Guinness. All dark beers have strong flavor profiles, but none are as smooth to drink as a Guinness.
My recommendation to a Canadian would be to have a Rickers Red on tap first. That is a pretty tasty beer. Again, the bar needs to be serious about keeping the beer fresh, lines and taps clean, glasses properly cleaned without soap residue. Crappy bar, crappy beer experience.