We are a Canadian Company that requires online payments via debit card "Interac" in Canada we are currently using moneris as our payment processor and WHMCS for our billing system. The module must allow customers to pay via canadian debit card.
We are using eselect plus on moneris.
WHMCS development information is available in this document Our development documentation can be found at http://docs.whmcs.com/Developer_Resources
Moneris development guides http://www.eselectplus.ca/en/downloadable-content