An LLC (Limited Liability Company) isn't a corporation. It is a vehicle with limited liability. An LLC may be taxed by the IRS as a C Corp or a partnership/S Corp (same thing for tax purposes). If the LLC has only a single owner ("member"), then it may be taxed as a "disregarded entity" (ie: sole proprietorship) so its income and losses pass throuh directly to its owners' tax return.

A corporation is a whole other mess of tax and accounting regardless of which side of the border you're on. Weirdly enough, a few provinces have ULCs - Unlimited Liability Corporations - which have useful tax propertes for American corporations looking to expand their operations northward.