I've nicked a few seeds so that I see white but I also see a little brown in the center where I nicked too much ( I used a palm sander on a few.)
Is the core completely white and does this color mean the seed is "dead".
I don't know the answer to your questions, but from what you write it doesn't sound like the seeds were very sturdy. Do you know what variety canna seeds you have? Not all varieties produce a viable seed, that is why to grow many of the hybrids you need to plant rhizomes. In any case if the seeds don't germinate within a couple of weeks they won't germinate at all.
Well,,, if you have a doubt. Get a good knife and cut one in half. If that's impracticle, just get a pair of pliers and crush one. If you find rotten stuff in the middle, then you have your answer.
I just got through nicking a batch of fresh seed and I found some brown stuff, though hard, in the middle.
I think the seeds are fine.