Agree with Rob_TO.
You do not actually have to apply for a PR TD (Permanent Resident Travel Document) in order to enter by land. However, if you do apply for a PR TD, they will see that you do not meet the RO (Residency Obligation) and revoke your PR status unless you have some really good H&C (Humane & Compassionate) grounds for not being able to meet the RO.
If you try to cross without a PR TD, you will have to answer questions by the immigration officers and although they must admit that you are still officially a PR and they must let you in, they can report you for not meeting the RO. If they report you, you can appeal it but without H&C grounds backing up this appeal, you will lose it eventually and lose your PR status.
If they for some reason do not report you as you enter Canada, there is a way to put your PR status back in good standing by staying in Canada for 2 years straight without leaving. At this point, you meet the RO again for the previous 5 years and can apply to renew your PR card. However, it may not be easy to stay in Canada for 2 years without a valid PR card. You may find yourself having problems getting health care and a drivers license and if you don't have a SIN, you can't work legally either. If you do have a SIN, you can work although some employers may not want to hire you without seeing your PR card.