We are not allowed to ship lithium polymer batteries internationally via Canada Post. How can I disable the Canada Post shipping method when the customer is international and they have certain items in their cart?

There is no feature to limit shipping services offered on a per product basis.
It could be custom programmed though.
I suggest a post in the developers forum, or reach out directly here - https://www.ecommercetemplates.com/developers.asp

Thanks,
David

Just an update if anyone is searching for the same; Mike at DLSS was able to write me a mod that does what we needed! Thanks Mike!