As long as you have a legal status in Canada, you may invite your parents to visit you. The visa officer mostly will focus on your parents' economic situations, such as bank deposit, employments, houses, etc. They may apply for 2 or 4 weeks, but as long as they come in, they will automatically can stay up to 6 months legally without extend their visa. Of course they can extend their visa at the end of 6 months. Good luck!
