If you have an RRSP or RRIF, the income isn't actually automatically deferred for US purposes. The income earned in an RRSP or RRIF is, in general, taxable for US purposes. In order to defer the income until you make distributions then Form 8833 Treaty-Based Retrun Position Disclousre Under Section 6114 should be included in your US tax return.
This election needs to be included in a timely filed US tax return (including extensions) otherwise the income from the RRSP, RRIF whether distributed or not is considered taxable income to the US regardless if not distributed.
Convention Between Canada and the United States of America
Article XVIII Pensions and Annuities
"7. A natural person who is a citizen or resident of a Contracting State and a beneficiary of a trust, company, organization or other arrangement that is a resident of the other Contracting State, generally exempt from income taxation in that other State and operated exclusively to provide pension, retirement or employee benefits may elect to defer taxation in the first-mentioned State, under rules established by the competent authority of that State, with respect to any income accrued in the plan but not distributed by the plan, until such time as and to the extent that a distribution is made from the plan or any plan substituted therefore.