What do you mean by "does not work"?
Have you optimised the Canon's settings to better suit VoIP?
The choice of ITSP may be important too.
I have a Brother MFC-J4510DW connected to an OBi110 in the UK. Works fine via Localphone to an ancient Sharp fax on a cable TV phone line in rural Japan.
Someone else will be along here soon to tell you that fax machines are yesterday's technology and suggest alternative methods.