I am importing a source CSV file, I don\'t know the source encoding and I can only see either � (ANSI encoding) or � (UTF8-without-BOM encoding)
It was answered in the comment. Did you try it?
http://msdn.microsoft.com/en-us/library/ms189941.aspx
Option DATAFILETYPE ='widenative'
Based on comment from Esailiga did the text get truncated before or after the bulk import. I agree it sounds like the CSV file itself is single byte. Unicode requires option DATAFILETYPE ='widenative'. If the CSV file is single byte the is not magic translation back.
What is too bad is é is extended ASCII and supported with SQL char so more evidence the problem is at the CSV.
SELECT CAST('é' AS char(1))
notice this works as extended ASCII (<255)
Sounds like you need to go back to the source.
The ? in SQL is unknown. Same as � in notepad.