Canadian processing is not as complex as international processing. There are five major banks and 3 payment processors, which are Paymentech, Nova and First Data.
If you are a start-up and would like compatibility with WHMCS, you may want to start with PayPal or 2CO and build processing history.
checked Merchant-Accounts.ca and they force you to pay for application fees now without knowing anything about the conditions offered with the merchant account, no contract viewing, nothing except the fees. It looks like they want to charge you first (even if they say they will refund you if you are not accepted) to hold you as client. Doesn't sound reasonable for me
Internetsecure is great -- note that it doesn't work with the latest versions of WHMCS though. Psigate is another option although their creditors / providers seem to be a lot more strict (which could be a good thing, I suppose).
I'm using the former.
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If you're just getting started, I'd consider solutions like internetsecure or 2CO. Best to ask them directly if they can integrate with WHMCS. Once you've got some processing history under your belt you can get in touch with Optimal Payments out of Montreal.. they have an excellent gateway that I've used since 2003. Great company.
Pioneer Payments | high risk merchant accounts
Processing credit card, electronic checks, and alternative payments
EU & offshore incorporations and bank accounts