Final answer:
The three people that M. Blondin talked to before Hercule Poirot at Chez Ma Tante were Monsieur G-, the Prefect of the Parisian police, the courier, and some third-rate Italians.
Step-by-step explanation:
According to the given references, the three people M. Blondin talked to before Hercule Poirot at Chez Ma Tante were Monsieur G-, the Prefect of the Parisian police, the courier, and some third-rate Italians. In the first reference, Monsieur G- enters the apartment, indicating that he was spoken to by M. Blondin.
In the second reference, Winterbourne's aunt mentions that the young lady is very intimate with third-rate Italians, suggesting that they were also spoken to before Poirot. Finally, in the third reference, Bobinôt, Bibi, and another person are laughing and seated at a table, indicating that they were also spoken to by M. Blondin.