there have been many threads on this.
You can be accepted from a visa-exempt country at the border with a PR app in progress. But it is up to the IO who you see at the border - it is up to the individual agents' discretion and you can be turned away.
Somethings that other posters have mentioned:
- it is much easier to get a VR or even just be allowed in for a visit if you are traveling by car from the US
- it seems to be easier to be allowed in for a visit if you arrive sometime late at night, whether by air or by car
-From what I have read, here and elsewhere, if you have a PR app already in progress, and the applicant wants to be admitted into Canada you need to provide 1)proof of the application - i.e. fee receipt, all correspondence received from CIC, and a copy of the application itself so that the IO can judge the likelihood of its approval. 2) proof of adequate income to support the applicant while they wait for the PR visa 3) proof of health insurance. and 4) it is much better if the sponsor is there at the border/customs with the applicant to tell their part of the story and to vouch for the validity of everything.
- you also need to have a return ticket, and/or proof of having been given leave at your job, and proof of owning or leasing a home, even if you are not planning on returning - these are ties to your home country and even if you ask to stay long-term, you may need to provide proof that you have a home and life to return to as you will only be a visitor in Canada. Also, it's probably a good idea to get health insurance to cover you while you are in Canada.
Of course, the IO may or may not ask for any of that proof. But if they do ask, and you cannot provide it, then that can be a problem. Many other posters have been totally successful crossing the border without really having to say much. The general consensus seems to be that you should be prepared with all of the evidence you might need, but should not mention it until asked by the IO. If you are waved through without a lot of questions, you will have 6 months, or whatever time the IO decides to give you. You can probably extend your visit through CPC-Vegreville after you arrive.