How can Canadian French characters be displayed correctly when using ANSI encoding?

We have a requirement to send a demographic file to a Canadian RRSP vendor using ANSI encoding that supports ASCII characters. However, when we use encodings such as ASCII or Windows-1252 in our XSLT template, all Canadian French special characters are replaced with either a question mark ('?') or a blank space. Alternatively, when we use UTF-8 encoding, the special characters display correctly, but the vendor is unable to load the file, as they require it in ANSI encoding.

Therefore, we are seeking methods to ensure Canadian French characters are properly displayed when using ANSI encoding.