They will generally know what a good GPA is for the different Canadian universities. They are not comparing you to USA students.
However, if you are looking to apply for PhD programs, you should know that your GPA is really not a large part of admissions. What is important is that you have demonstrated the ability to be a successful researcher. I knew somebody who was accepted to a good PhD program with a GPA of 2.7, because they had top-notch research skills, and a letter of recommendation from one of the top people in their field telling about those skills.
Some PhD programs have a minimum GPA requirement for entry to the PhD program, and if your grades in the major in which you want to do your PhD are not high, that may weaken your application.
Still, the most important parts of your application are your CV, your letters of recommendation, and your cover letter.