Amex specific international Paypal fee - Buying

Making a sizable purchase from a Canadian seller (I am in US / have US amex). Seeing note card issuer fees not yet included for my Amex with the full corresponding CAD price.

When I switch to my other non-Amex cards or checking account, I see the USD price, using Paypal’s suboptimal conversion rate with no mention of additional fees.

My question - does anybody definitively know what these fees are made up of? It looks like Amex conversion is slightly more favorable than PP, but concerned I could get hit with an additional buyers fee with the Amex. Appreciate any perspective!