Can a US company sue a Canadian company?

Technically you can sue any company in the world, but will it get anywhere? When you sue a Canadian company, you pretty much have 1 in a million chance of getting anywhere due to their different legal system, not to mention their justification for lawsuits which are not as "buyer centric" as the US system. Especially when a US company is involved, you have very little pull in the law unless the company is also registered in the US. It is always advisable to come into a settlement than taking the lawsuit route. Not to mention the time and cost involved.