You could go via YUL; it's available in C for your dates. If you want to book online, you will need to book it via Destina.ca because the YOW/YUL segments are all Y Dash-8 and AC.com will automatically tell you no 'Restricted Exec class' available if you just enter YOW/FRA.

I suggest you go via YUL because this route will be operated with A330 for the next few weeks with the 74E in maintenance in SIN.

Let me try and see whether it prices out on Destina.ca.