If your pr is expired, you can leave Canada. There is no problem. But when you will enter Canada, you have to have your renewed PR. You have two option. You can renew your pr from Canada and leave Canada with expired pr card. When pr will come in your Canada address, tell your family to send pr to you, and then you can come into Canada. The second option is before you come you can take entry visa from Singapore visa office. But you have to have apply the visa at least 4-6 weeks ago to get passport back in proper time.