Yes you can, but there are some caveats. Here's the basic run down:
1. If you are traveling by private car, all you need to show at the border is your CoPR.
2. If you traveling by commerical vehicle, such as, airplane, boat, bus, or train, you will have to have a travel document.
However, if you are from a visa-exempt country, you can *usually* get away with traveling with only your CoPR if you are using commerical transportation. Most of the time this will work because legally you are a PR of Canada regardless of having a pr card. The card is just a form of id verification, it's not something that decides your status. For example, if you lose your pr card, you are still a permanent resident.
Here's where it gets a bit tricky. When you travel on commerical transportation, they are suppose to check your documents and status before you board. So, if you are a PR, they are supposed to ask for id to confirm this. Commerical transportation companies are only supposed to accept pr cards as ID. Thus, the whole, without the pr card they shouldn't let you on. However, if you are from a visa exempt country, they will almost never ask you about your immigration status and will simply ask for you passport just to confirm your ID, not your immigration status. Now the border guards at the Canadian border ARE allowed to accept the CoPR as an ID for immigration status. So, once you get to Canada you shouldn't have any issues.
Please be aware that this is actually supposed to be changing this year and they are going to start to enforce the checking of the pr cards:
http://www.cic.gc.ca/english/newcomers/about-pr.asp
Now, my recent experience, about two weeks ago, was exactly the what I described above. I'm from a visa exempt country and flew back there. The airline didn't bother to check my immigration status and only looked at my passport for my regular id. When I got to YVR, I had to go through secondary customs. There, the border officer asked me my immigration status. When I replied PR, he asked me where my pr card was. I explained I did my landing a month earlier and was still waiting for my card. I then said I have my CoPR and he asked to see that. He took a look and then passed me through.
If you are going to be leaving Canada for more than a few weeks, you should probably get the travel document. That shouldn't be a problem because it's only supposed to take about 1-2 weeks to get it. The reason people have trouble with the travel documents is that you can't get one inside of Canada, you can only apply for one outside of Canada. So, if you are going to be out of Canada for only a week, you won't have enough time to get the travel document before you want to return to Canada. It's not the best setup.