I have very limited experience with Canadian scene but in the US most of the lab work (postdoctoral) is done by Indians and/or Chinese. Postdoc positions are transient jobs meant to give folks some additional focused experience in the laboratory while they make up their mind about what they want to do. So salary is not a big issue. However, one could negotiate higher salary if there is much demand for the discipline. In the US, salaries depend on the type of visa: people with J1 visas can be taken for a ride since their salaries are not regulated. Those with H1 visas are guaranteed a minimum level... One could negotiate for higher pay at the time of interview. I cam to Canada with expertise in materials science so I was in a good position to bargain for higher pay. In Canada, salaries are around 30-36k for the startup postdoc. It is not a wise idea to become a professional postdoc. Most people plan on moving into longer-term positions within three years. I spent a year and half as postdoc in Canada before moving into a continuing position.