It could go either way... Mazda expected to sell 75,000 Mz6s for 2003 and are closing in on about 61-65k cars by the end of the month. Compared to 626 sales, the 6 did not sell any differently. The 6 actually could have sold much better if Mazda didn't make package options so difficult...
Since the Protege sells anywhere between 70-80k cars per year, the Mz3 should meet or beat those expectations. I'd guess "beat" since the Mz3 offers A LOT more content for it's price point compared to the Civic and Corolla especially for customers willing to spend more than 18k for a compact car with the Jetta the only car offering similar features in a less reliable package. An added bonus, the Mazda3's package options are much easier to configure than the 6's...