The US requires all citizens and green card holders to file tax returns and reports on non-US financial accounts no matter where in the world they live. The only exceptions are those whose income is below the minimum, and those who have less than $10,000 in all of their non-US financial accounts combined.
If you are a US citizen or green card holder these requirements, expecially those related to financial accounts, can be a big problem.
There are hefty, very hefty, fines for not filing reports on these financial accounts. There is rarely tax owing. For US citizens working in Canada it is possible to take credit for taxes paid to Canada, including Canada Pension Plan and Employment Insurance. Because the tax rates are generally similar the CPP and EI plus Canadian income tax is usually more than the US income tax would be. I have only seen two cases where tax was due on the US return after taking credit for taxes paid to Canada. One was about $50 and was caused by the sale of a condo in Canada. The other was caused by sale of a house in Canada by a retiree. The taxpayer used charitable contributions to wipe out Canadian tax on the sale. On her US return she was only allowed half as much for her charitable contributions so there was a large tax owing.
If you are liable for US taxes, to regularize your situation the IRS wants to see 6 years of returns, including those for financial accounts if the total comes over 10,000 in any one year.
Please remember that the US government has a long memory for taxes owing. There have been a couple of cases in recent years where someone who was living in Canada decided to visit the US in the mistaken belief that the US government had forgotten an old criminal charge. In both cases the visitor was sent to answer a murder charge from more than 25 years before. It would be foolish to believe that they would forget something that would result in taxes being paid.
If you are in this situation I can prepare the forms for you. I will need the Canadian returns and the information on your financial accounts. Often preparing the pages about financial matters is more work than preparing the tax forms.