Sorry, I don't know about any good Montessori's in Troy - but I can tell you about my girlfriends preschool. It is called Beautiful Savior Early Learning Center (BSELC) and is part of the Beautiful Savior Lutheran Church that is on Adams Rd. between Long Lake and Square Lake roads. The phone number is ###-###-####. Joan Hempke is the administrator, so she would be the person to talk to (she is at that number). My girlfriend highly recommends the program. She says they do teach some basic Christian concepts along with the other basic learning skills (numbers, alphabet, etc), but nothing specific to any denomination is taught.
Also, I was intrigued by the fact that you are new to Detroit and your first language is French. I speak French as my second language (I majored in it at College - but haven't done much with it in the past 7 years or so). I could definitely use the practice - both written and oral. Please email me if you are interested in conversing.