I took as muchj of a look at the 3 as I could, but the sales guy got pissed when I tried to take off the doors .
It looked like it has 5x7's all around. where the protege only had them in the front. Also the hatch and sedan have the same speaker locations now so it seems to be 5x7's all around for both models.
i was thinking abt an adapter would work but i don;t like the work and time i spend on it, it will be muhc better and faster just to get a new pair or yet a better pair
The speaker is a 6x8 in all four doors, but most 5x7 speakers work for both. There are adapters you can buy to use a 6.5" or 5.25". Check out this thread for info on the Mazda 3 audio system with full details: