I have a very similar situation. My citizenship application is stuck, nothing is being processed. My PR card is expired and I applied for renewal.
However, you can still travel under certain circumstances. I asked CBSA via phone.
Common carriers, like airlines, won't let you enter Canada on an expired PR card. But as long as you can somehow travel on your passport to Canada, you should be fine. CBSA says as long as you have a valid PR status, they'll let you in, even if your PR card is expired. But that only works when you're there with CBSA, not with the airline agents. One scenario is crossing the border to the US via a private car, you can return to Canada via a private car as long as you can prove you have a valid PR status.