Since you are a British citizen, you will most likely be let in with no problems as a visitor. Do not lie to the border agent. Many people come to Canada as a visitor after submitting their outland PR application, ordinarily with no problem if they are from a visa-exempt country (as you are). Have a copy of the forms or proof that you have submitted the PR app, such as a copy of the receipt or proof your sponsor was approved; a return ticket with a specific date; proof of any ties to the UK. Probably the border agent will not ask to see any of this, but it is best to be prepared. You have to be clear that you are just coming to Canada to visit, and will leave if the PR application is denied. Do not say you are moving to Canada - because then yes, you might be denied entry. You will probably be given 6 months at the border; if not, the border agent will stamp your passport with the date you have to leave by. You can apply to extend this stay about one month before it expires.