Depends on wehat seeds you have--see chart at site linked below.
You can Google "seed viability chart" --add either flower or vegetable aas the first word if you want. There is a LOT of info out there.
You can always do a germination test, too, using damp paper towels-- if you have enough to spare of the seed you are testing.
Every few years or so I take all my old leftover flower seed to a back corner of the yard -- where I had had a compost pile, say, so there is bare ground -- and just scatter all the contents of the packets around to see what comes up!

Here is a link that might be useful: Seed viability chart

Give the seeds a chance! What is the worst thing that could happen?

I have read that seeds that are really really really old still can produce sprouts. So give them a try. Three years is not very long.