One requirement for a visitor visa is that the applicant should be able to prove that he/she would be coming back to his home country. Your case, the PR application might make it a little difficult to convince the visa officer of the same.
So, when applying ensure that you have a good enough reason for applying the visa, may be a wedding in the family or any other such event. And, back it up with documents and an invitation letter having details of the event or reason.
Impact on PR application, ensure the information you provide for visitor visa application is in sync with what you provided for the PR application. For instance, few give a medical reason for showing ties with their home country, that they have an appointment or any such thing with the doctor. This can to an extent impact the PR application if there is no mention of the medical history in PR application. So, ensure what ever reason you give for visitor visa application is either no way related(like wedding event) to or is already shared(like medical history) with CIC in the PR application.
