As far as I know, the alcohol content is the same here. The beer is brewed in Canada, and the "essence" is shipped from Ireland to add to the beer before packaging.
I drank a lot of Guinness in Ireland (it tasted the same), and when I go to the pub with the guys from my neighborhood (one from Dublin, 2 from near Belfast) they say the Guinness tastes the same. But we go to a good Irish pub that cleans their lines regularly and pours a LOT of Guinness, so it is always very fresh.
And for what it's worth, my neighbor's dad visits from Dublin every year and stays for a month or more (he'll be here again in 5 weeks). He says the Guinness at Wilde Rover in Kirkland is as good as the Guinness at Buglers (pronounced BUG-lers, not BYOO-glers) in Dublin. That could just mean that Buglers pours a crappy pint though