Hi Whatdog,
The common symptoms will be: Anxiety, respiratory problems, (being the first thing you may notice as cyanide prevents oxygen from circulation at a cellular level) staggering, convulsions, collapse and death. There is a very small window to get your pet to the vet for an antidote once the symptoms begin, but as already said, your dog would need to take in quite an amount to stop his body from counteracting the small amounts of cyanide,
Unfortunately, you say there are a lot of cherry trees around your area, just make sure they don't become a play thing for him, I know it can be hard when our dogs spend their lives with noses to the ground, but do your best to keep him on you and something else whilst passing the trees.