Do both the federal foreign buyer ban and Ontario's non-resident speculation tax apply to the same purchase?

Yes, potentially both, and this is an important point of confusion to clear up, since people sometimes assume the two rules are really the same thing described two different ways. They are not - the federal ban and Ontario's Non-Resident Speculation Tax are separate regimes, from different levels of government, with their own definitions, exemptions, and consequences, and a single purchase can be affected by one, the other, both, or neither, depending on the specific facts.

If a foreign national is not exempt from the federal ban, meaning the purchase is permitted at all, that same purchase could still be subject to Ontario's tax on top of the general land transfer tax, unless a separate NRST exemption happens to apply. Conversely, someone exempt from the federal ban is not automatically exempt from NRST, and someone exempt from NRST is not automatically exempt from the federal ban - each needs to be worked through on its own.

Have your lawyer assess both the federal ban and Ontario's NRST separately for any purchase involving a non-Canadian buyer, rather than assuming clearing one clears the other.