Those of you who are visa exempt countries and will try to cross the border without PR card; couple suggestions, as I did that 3 times already using both land borders and airports:
1- You may or you may not have problems depending on the officer, there is a lot of subjectivity on their actions. But eventually you will be let in.
2- The major problem that may arise is they can send you to the secondary, and you may have to wait an hour over there. ( It did happen to me)
3- They may refuse to use your COPR claiming it is not a travel document as it is written on that document (It did happen to me)
4- DO NOT SHOW YOUR COPR TILL THEY ASK YOU if you are using airports or crossing land borders using bus. First show your passport to the officer, he/she will find out your visa on your passport, while doing that, explain him/her you are waiting for your PR card, he/she may simply let you in after finding you in the system, or he/she may ask you to show her COPR, then show it. Be prepared to answer "What are you going to do today?" type of questions.
5- If you use your own vehicle or rental car, PUT YOUR COPR INSIDE YOUR PASSPORT and give it to the office and be prepared to explain your purpose. There are cars behind you, and they don't want you to slow down the traffic. Be prepared to document your intention of visit. For instance, if you want to search for apartments to rent, have couple of them printed next to you so you can show it (It did happen to me)
6- If you use your own vehicle not rental, they may tell you need to import the vehicle otherwise they cannot let you in. That is not true as long as you confirm him/her the vehicle will be returned right away or within 45 days you are fine.
7- If your trip to Canada once again temporary; be prepared to answer "When are you moving in Canada permanently" type of questions. Even though, they are not supposed to question your intention as it is not part of the PR requirements; they can/and they do.
8- Don't book connecting flights just after your landing within 1 hour. You may need up to 2 hours since they can send you secondary as they wish to do.
9- Don't use a foreign address in your customs form, use the address you gave when you land at first time. Otherwise they can claim your visit will not be counted against your required 2 year stay out of 5 years. And they will admit you as visitor. (It did happen to me, I am not sure if it is even possible)