Communications law is a complex subject. In your case, you have the added issue of import/export regulations. I suggest you engage a competent attorney to guide you through these matters. Here are my answers based on my understanding of the questions you have raised. Please accept that I am not acting as your attorney.
A transmitter that is capable of being operated only on the frequencies authorized to amateur radio operators under FCC jurisdiction, does not require any approval by the FCC prior to being sold by the manufacturer. However, from a commercial liability perspective, the manufacturer should ensure that the transmitter allows the amateur radio operator to be in compliance with the part 97 bandwidth, spectral purity, and power output requirements.
A transceiver, on the other hand, will be subject to type 15 compliance requirements but typically only due to the receiver portion of the radio.
An external RF power amplifier that will be marketed for amateur radio use is required to be certified by the FCC as described in part 97 (which further references part 2).
Industry Canada has no jurisdiction in those geographies governed by FCC regulations so any IC approval is meaningless and therefore not required.
Depending on the construction of the intended transmitter, some state or local jurisdictions may require additional electrical safety compliance through UL or ETL testing and certification, for example.
...part 15 licensed devices, there's special FCC certification...
This is not technically accurate. Part 15 covers unlicensed devices. There are three levels of required compliance, the correct one of which depends on the applicable section of the code:
The manufacturer uses a test lab accepted by the FCC to measure and document that the requirements have been met.
Declaration of Conformity
The manufacturer issues a formal statement to the FCC that the device has been tested in an accepted lab and that it is in compliance with the regulations.
The manufacturer performs the necessary tests and confirms that the device conforms to the regulations. No notification is given to the FCC.