If someone in Canada sues a US citizen, is that case tried in the US or Canada? I'm in the US & want to know if I'd have to pay the legal fees if lose

It can be tried in either if the defendant has enough contacts with the place to confer jurisdiction upon it (here I'm assuming that Canadian law is the same as U.S. law), but where the case is brought does not determine what substantive law applies.  If you are sued in a U.S. court over an accident that took place in Canada, for example, it is likely that Canadian substantive law (as opposed to procedural law, like how liong you have to oppose a motion, etc.) would apply even though the suit is taking place in the U.S.  In that case, which law applies to the attorneys' fee question would depend on whether the basis (whether based on contract or statute or court rule) on which fees are sought is substantive or procedural.  My gut says that this is a substantive issue, not a procedural one, but I'm not 100% certain.