Petro-Canada has it's own brand of additive that works much the same. Can't remember it's name off-hand.
I can't find a Chevron station in Alberta, but the 91 Petro-Canada seems to do a great job.
BTW, Canadians should avoid Shell gas at all costs. Shell just admitted that they put a filler-additive int heir gasoline that wrecked thouands of gauge sending units in cars.
I never bought Shell for many other reasons (worst of the worst in human rights in foreign nations) but even I was surprised to find the crap that they've done to Canadian consumers.
It doesn't matter to me that they've "fixed" the "problem" as they ripped off people in the first place. Scumbags that won't get one cent of my money.
Also for us Canucks, Petro-Canada is the only Canadian owned gasoline retailer (fully integrated, actually), so the profits at least stay home.
1998 C230 "Black Betty"