Have reviewed your install and the error message immediately set with the IPN is as follows.
'errorText' => 'Authorize.net ARB API handles only USD, not CAD',
You need to be sure you're sending Authorize.net USD, but displaying CAD. This is done by adjusting the currency within CBSubs > Settings > Global.
Their AIM (single payments) supports multiple currencies, but their ARB (recurring) does not and must be sent as USD in most cases. So you'll need to use the below configuration to ensure Authorize.net is always working with USD.
Main Currency: US Dollar
Multi-currency mode: Secondary Currency: Canadian Dollar
This also seams to be dependent on the processor you're using. Please see the ARB API documentation below. Then review the "Accepted Currencies" chapter.
www.authorize.net/support/ARB_guide.pdf