They could publish the reviews today, but then they would have to pay a lot of money to Canon.
That's not how the industry works. That's not how any industry works.
If you've signed an actual NDA, which is a legally binding contract stating you will not talk about [subject] until a ccertain point (or simply ever), then yes, breaking that contract may mean you are subject to a lawsuit, whether you broke the terms of the NDA or not is very quick and simple to prove, and you'll be paying a huge fine and/or getting some time behind bars, depending on the exact nature of the subject at hand.
... But that requires the manufacturer to spend a lot of time and money drawing up legally sound contracts, getting copies posted off and signed, everyone filing everything correctly, and nobody can be bothered. It also opens up the possibility of leaks as if you send someone a contract saying "you will not talk about the R3 until 11am on the 14th", and then that person simply does not agree to sign that contract... well, you've just told them the R3 is coming and what kind of time frame it should be arriving. You've leaked yourself.
What actually happens, in this and every other industry you can name, is manufacturers strike non-binding embargos with outlets and influencers. An embargo doesn't require anything to be signed like an NDA does. If someone breaks the embargo you can't level any kind of charges against them, but outlets
won't break the embargo because they know if they do you'll never cooperate with them again. The threat of financial penalty is not there; nobody would have to pay Canon a single penny if they set an R3 or 100-400 hands-on video live a half day early, for example. But Canon would never send that channel a review unit ever again. They'd never invite them to press events again. They'd never give them any support reviewing any further products. If you break an embargo, that's it, you're blacklisted by that company. Other companies will also notice that you broke embargo and they will stop working with you, too. And if a channel, site or magazine can't get review units sent to them, they are pretty much out of business; very few people can afford to buy every product they want or need to review, and even when they can afford it, the nature of coverage now is so focused on being the first to publish that waiting for a retail unit to be delivered often means your review will not get enough traffic to make any money.
This is also why those outlets and channels which always have a ''review'' ready to go within minutes of announcement must always be taken with the largest barrel of salt you can fathom. They're never under
contract to suck up to the manufacturer—nobody is ever "paid off", and as a side note, accusing someone of being paid off or secretly under contract is in fact illegal, yes, even 'just' in a youtube comment, so nobody should ever do that—but they are under
pressure to not rock the boat much. Manufacturers will blacklist you for breaking embargo, for giving one product a negative review, or simply because you told a bad joke in the bar after a press event one time, so every outlet and channel
does have incentive to play nice and go easy on everything. It's just not a direct financial penalty incentive. That's why you so rarely hear anyone say any part of a new product is actually "bad", just "average" at worst. It's the old 7-10 scale: nothing is allowed to be given less than a 7/10 or you'll never get work again.
So, no, nobody would have to
pay any money to Canon. But if they break the embargo with a company of that size they'll struggle to produce work again, and cease
earning money.
(I've signed more NDAs in my lifetime than I care to remember and I've also been blacklisted by a fair few companies, so believe me when I say the pressure manufacturers put on outlets is very, very real.)