I tried to combine a circular polarizer with a linear. I noticed a heavy shift towards pruple-lilac at almost full polarization (very dark), so I imagine this color shift will be visible on film or digital as well. However, if the degree of polarisation is decreased the lilac tone disappears. BW film is probably most suited at the extreme end. (Hoya polarizers)
Im not sure about your cameras but both linear and circualar works fine with the AF on my Eos50.