ACH Vendor Payments - Dual Currency?

We currently using ACH payments for our vendors in Canada and US from a Canadian Bank (RBC). Everything has been working great, except I am trying to setup something for vendors that request payment in both CAD and USD. Currently we have Canadian vendors with a Canadian bank in CAD and US vendors with a US bank in USD. We have a couple vendors, mainly freight companies, that want to be paid in either CAD or USD. The vendors have two separate Canadian Bank accounts, a CAD account and a USD account. I can setup the vendors to use one or the other, but I have not found a way to have both payments for the same vendor. Has anyone done this before? How did you set it up?
Thanks