Who files Section 217 return (pensions)?

Not as a matter of course. Canadian pension, retirement and benefit income paid to a non-resident is subject to flat withholding at source, and for many recipients that withholding is the end of it. The elective return under Section 217 is for the recipients who would do better being taxed at graduated rates on the year as a whole than at the flat rate on each payment. Whether you are one of them is a calculation, not a status. It is worked out before the return is prepared, because the election is a choice and not the default outcome.

No. The election is all-or-nothing across the eligible income for the year, so it is not a matter of picking the payments where the flat withholding looks worst and leaving the rest alone. That is why the arithmetic has to be done on the whole of the eligible income together. A recipient with two or three Canadian sources can easily find that the election helps on one and hurts on another, and what matters is only the combined result once every eligible amount is inside it.

By running the year both ways before filing. One way is the flat withholding already taken on the gross payments. The other is the graduated-rate result on the eligible income as a whole. The election is worth making only where the second is better than the first, and because it is all-or-nothing, the comparison has to cover all the eligible income for the year rather than a sample of it. That comparison is the substance of the work on this return. The filing itself follows from the answer.

Yes, and this is why the election is treated as a calculation rather than a default. If the graduated-rate result on the year is higher than the flat withholding already taken, electing simply converts a closed position into a larger liability. Because the election is all-or-nothing across the eligible income, a recipient cannot elect and then carve out the parts that turned out badly. Establishing which way round it falls is the first piece of work, and on a reasonable number of pension files the answer is not to elect at all.

The two things are separate. The payer withholds as the pension is paid, on the amount paid. The elective return deals with the year after the fact, and recovers withholding through the assessment rather than by switching it off at source. Reducing what is taken from each payment is a separate approach to the tax authority, made in advance and decided on its own merits. So a recipient who elects for one year should not expect the following year's payments to arrive any differently unless that separate step has been taken.

Often it is, and that is the case where the election tends to help most. Flat withholding takes the same proportion of each payment regardless of how small the year's total income is, whereas graduated rates start low. A recipient whose only Canadian income is pension and benefit amounts is therefore the recipient most likely to find the graduated result better than the flat charge. It still has to be calculated rather than assumed, but this is the shape of file where the election usually earns its keep.

A bilateral agreement that allocates taxing rights between two countries so the same income is not taxed twice without relief. It decides which country may tax each income type, caps withholding rates at source, and supplies a tie-breaker when both countries consider you resident. A treaty does not reduce tax automatically — you claim its benefit on a return, a withholding form or a residency certificate. Tax treaty vs domestic law shows how the two interact.

It is legal. Two countries can each have a valid claim on the same income — one because the income arose there, the other because you live there — and nothing prohibits both from exercising it. What exists instead is relief: tax treaties allocate the claim, and domestic law gives a credit for foreign tax paid. The relief is not automatic, though. It is claimed on a return, and unclaimed relief is simply lost. See how double taxation is relieved.