As mentioned above, the contributions were made to my account prior to becoming a US resident. I am copying a paragraph from the link I provided, it sounds like it's not taxable:
Foreign Contributions while a Nonresident Alien
Your contributions and your employer's contributions are not part of your Cost if the contribution was based on compensation for services performed outside the United States while you were a nonresident alien and not subject to income tax under the laws of the United States or any foreign country (but only if the contribution would have been taxable if paid as cash compensation when the services were performed).
Foreign Contributions while a Nonresident Alien
https://www.irs.gov/businesses/the-taxation-of-foreign-pension-and-annuity-distributions
In the IRS Publication - The Taxation of Foreign Pension and Annuity Distributions that you cite also states - As a general rule, the pension/annuity articles of most tax treaties allow the country of residence (as determined by the residency article) to tax the pension or annuity under its domestic laws. This is true unless a treaty provision specifically amends that treatment. Some treaties, for example, provide that the country of residence may not tax amounts that would not have been taxable by the other country if you were a resident of that country.
Per the Treaty between the United States and Canada in ARTICLE XVIII Pensions and Annuities it states –
Pensions and annuities arising in a Contracting State and paid to a resident of the other Contracting State may be taxed in that other State, but the amount of any pension included in income for the purposes of taxation in that other State shall not exceed the amount that would be included in the first-mentioned State if the recipient were a resident thereof.
Based on the Treaty you pension payments are fully taxable on your Form 1040 up to the amount it would have been taxed if you were a resident of Canada. That you cite also states that
