Retirement tax questions

If a US resident having RRSP in Canada, when the person takes a distribution of RRSP, the Canadian government is always holding 25% of the distribution as non-resident tax. My questions are: 1) how could it be "taxed only in the United States"? Any special way leads to get the tax credit; 2) if the person reports it in the income section of RRSP, how could it be treated as social security benefits?