The USA just made some rule changes recently, and a HUGE number of dual citizens here in Canada are all upset about it. Apparently August was the deadline to get caught up; otherwise, some serious fines kick in.
First, yes, they have to file. A lady I work with, her brother hasn’t lived in the USA since he was 5; he’s like dozens of others on the news here - he faces several $10,000 fines (or jail time) if the border guards decide to be dicks next time he visits the states. Just to find an accountant who could do his taxes on short notice (assuming he could find one) would cost thousands of dollars - all for some guy making a basic, normal living wage. Some experts have suggested writing to the IRS and asking for more time, but all this does is draw attention to yourself and commit you to spending the thousands on a tax attorney.
Apparently, one of the “gotcha’s” is reporting foreign assets (i.e. not in the USA) of greater than $100,000 if I understand the news story right, whether you owe taxes or not. Many Canadians over 40 will have 1 or 2 retirement funds (RRSP, like a IRA or 401K) that exceed $100,000. A house and or cottage will exceed that too. There’s a $10,000 fine each for not reporting such assets. Likely, the tax paid to Canada, which I understand would be deducted from tax owed to the USA, means the person would pay no income tax.
The law is supposed to nail those millionaires who secrete their cash in foreign accounts - if the country catches you hiding foreign assets, they’ll nail you and pay. But if you cross the border and the guard notices “born in the USA” on your passport, he might look you up in the US database and see you have no return filed - you screwed if he wants to be a dick. Of course, if you renounce your US citizenship now, that still does not relieve you of the prior obligations to file; it just brings you to the attention of the US authorities. The US has made no comment to clarify the situation, which does not inspire confidence in their willingness to compromise.
Finally, a lot of Canadian banks have US subsidiaries; this puts them under an obligation to cooperate with the US and reveal personal details about the finances of Canadians who may have dual citizenship (welcome to 1984); so the US will know about a dual’s savings account, mortgaged home, etc. Plus, possibly they can force the bank to turn over those assets to pay fines… USA takes your retirement savings, and you are then on the hook to pay the Canadian government the withdrawal taxes for that fund… Aren’t terrorist finance laws wonderful.
I’m sure if you google for it you can find plenty of recent Candian news stories.