Leave the client id part blank. You won't get a client id until you receive your AOR.
As for crossing the border, carrying a copy of the receipt is a good idea. My husband (U.S. citizen) rarely had any issues coming to visit me. Once in awhile they did want to see some form of proof that he would be returning to the US and not trying to live in Canada illegally. Pay stubs, a copy of a lease on an apartment, bills, etc. are all good things to have. Also carry proof that you have an application in process, including any communications received from CIC.
Never bring more clothing or personal belongings than you would need for the length of time that you tell Canada Customs that you will be staying. That will raise red flags for sure. Nobody travels with a blender and eight pairs of pants for a weekend.
