@AndreC1 , generally each tax year stands on its own. Thus you should file an amended return recognize the unreported income. Even though I do not know the full circumstances and facts, I would prima facie disagree with the accountant advice.( to not file an amended return)
General rule is if your AGI or Taxable income for the year does not change by amending a return, then there is no need to file. It is just more paperwork to process.
Also did you pay any taxes to Canada on this interest ? That may also play into your tax liabilities.
Is there more I can do for you?
