I don't think you can combine those two, because there is, as you mentioned, significant overlap. One would hope that all of the transactions between Canada and the OFC, as reported on the T106 forms, have been captured by Canadian financial institutions that have to report any transaction out of or into Canada of more than $10,000. There should be quite a bit of overlap if the system works.
The amount reported on the T106, if we take it at face value that corporations have been honest and fully transparent in reporting their transactions with affiliates, is in my opinion probably the most reliable, because the EFT amounts probably include transactions from corporations and with corporations that may have little to do with affiliates. These could be pure economic transactions, but no one can be sure.