1. US citizens report worldwide income, so Canadian Pension and Retirement funds totaling $25K in USD are reported on the US 1040 regardless of filing Canada return. They might owe USD on it.

2. Do they need to file Canadian return? There might be CAD $ taxes withheld.

3. Even if they don't file a CAD return, they can still file 1116 since the tax they paid was the withholdings, if any.