Hey There,
Firstly and most importantly, you have met the 730 residency obligation.(because you lived in Canada for 3 years.) This is the most important and makes your situation easy.
So to enter Canada, if you are traveling by commercial transport into Canada (air, bus, rail, etc) then you need a VALID PR CARD.
If you are traveling by pedestrian crossing or private car, you can enter Canada with your expired PR card with no issue (though processing may take a few extra minutes and they may make you go to secondary.) Once in Canada, you can apply for a PR card.
If you want to travel by commercial transport and your PR card is expired, you will need to apply for a PR Travel Document (issued by a Canadian Embassy/Consulate) However, going in by road is just way easier and more hassle free.
Just remember as a Canadian PR, you PR card, expired or not is proof of your status. Once your status is established, IO's, by law, must allow you into Canada without exception.
Hope this helps and let me know if you have any questions.