When you file your income taxes, the withheld amount will be applied against any income tax owed on your taxable income, including the RRSP withdrawal. If the withheld amount is more than the income tax owing, you'll get a refund.
Yes, you would need to enter your worldwide income, though you will not be taxed on it.
You would have to contact the CRA to see if your tax obligation can be moved to Poland.
