Doing it by the book, you should contact a visa office in the US to report your PR card lost and apply for a PR travel document, see http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=47&top=10
However, I don't think you have enough time to get a PR travel document before Friday. As your passport is visa exempt, the airline may still let you fly. The eTA hard requirement has been pushed back until November 9th, see http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=1235&top=16
Should the airline refuse, you could attempt to fly to Buffalo and crossing over by land from the US.