One of the many cases that now clarify this topic include Easthaven, Ltd. v. Nutrisystem.com Inc., 2001 CanLII 27992 (ON SC), http://canlii.ca/t/1vz4l retrieved on 2014-09-19, which states at para. 29 (where the 'person' is referring a company whose presence was based on Internet activity in Canada):
The court held that general jurisdiction could be found in such a case [with an Internet company] only if the person was domiciled in the jurisdiction or his activities there were "substantial" or "continuous and systematic".
Jurisdiction can also arise for specific subject matter, as in the case here involving Netflix and the CRTC, by certain statute or treaty (viz. the NAFTA provisions for cultural accommodations for media). Of course a Court in Canada could just assume jurisdiction and give a paper judgment - the question then becomes whether an American court would recognize the judgment through the process called comity. With extremely rare exceptions between Canada and the USA, the Courts will recognize the judgments reciprocally.
There is also nothing stopping the CRTC from bringing an action in the USA based on violations that occurred in Canada. The applicable law may be different from the law of the jurisdiction that addresses the allegations of wrongdoing (i.e. it may be Canadian law that applies, but heard by an American Court, or vice versa). In any case an operation being abroad is not a defence from wrongdoing - notwithstanding e.g. extraterritorial immunity arising from a treaty.