How is a Roth IRA treated for Canadian tax purposes after I move to Canada?

A Roth IRA doesn't automatically get treated by Canada the way a TFSA is, even though the two accounts work similarly in the US and Canada respectively, contributions made after tax, with tax-free growth and withdrawals. Without taking any steps, Canada could otherwise tax the growth inside a Roth IRA or its eventual withdrawals, since Canadian tax law doesn't have a built-in category that automatically recognizes a foreign account's tax-free status just because it functions like one.

The Canada-US tax treaty addresses this specifically, allowing a Canadian resident to elect to preserve the Roth IRA's tax-free treatment for Canadian purposes as well, so that growth and qualifying withdrawals remain untaxed in Canada in the same way they are in the US. This protection isn't automatic, it depends on making the right election, discussed further elsewhere, and on not doing things that could jeopardize the treaty protection, such as making new contributions to the account after becoming a Canadian resident.

Because the default Canadian tax treatment of a Roth IRA, absent the election, is considerably less favourable than what most people assume, anyone holding one who becomes a Canadian resident should deal with this promptly rather than assuming it's automatically covered like a TFSA.