I wouldn’t give too much on this support article. It’s obviously just a copy & paste of the corresponding FP2 article (with minor adaptions):
The FP2 doesn’t support any of the 4G LTE bands used in the USA, so “4G(LTE) will not work” was correct for the FP2. But the FP3 supports way more bands, including some used in the USA.
Also, the supported 3G bands listed there don’t match the ones in the tech specs on the official product page.
(I’m aware this thread is about Canada. Just wanted to point out that “official” information from Fairphone is not necessarily correct.)