If you have applied for PGWP and waiting for a decision, you can travel to outside Canada and come back. You may enter as a visitor, and you can work without a work permit until a decision is made on the application.

A border officer will have some questions for you when you return to Canada. The officer may ask you for proof that you applied for a post-graduation work permit, such as a copy of your application or the fee payment receipt.

Remember: You must have a valid Visa on your passport.

Source: https://ircc.canada.ca/english/helpcentre/answer.asp?qnum=1309

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