You usually have the right to enter the country as a Pakistani citizen. However, it could be a little more difficult and time-consuming to prove your citizenship to the border official if you don't have a valid passport.
If your NICOP is expired, it will be difficult to travel to Pakistan, though. No airline will let you board the flight if your passport isn't valid. The NICOP is an important document that not only serves as proof of your Pakistani citizenship but also facilitates ease of travel between Pakistan and other countries. However, if your NICOP has expired, you may face issues at immigration checkpoints, both in Canada and upon arrival in Pakistan. You do have the right to enter Pakistan as a citizen of Pakistan, but the airline cannot confirm this without a valid passport, so they will play it safe and refuse you boarding. If you are refused entry, they will have to pay for your return flight and impose a fine.
The best course of action is to renew your NICOP before traveling. The renewal process can be done online or through the nearest Pakistani consulate or embassy in Canada. Renewing your NICOP in advance ensures that you avoid any issues during your travel and arrival in Pakistan.