Tarrifs and USPS forwarders - Cross boarder Posh US selling

I use DYK Post to ship items cross listed to Poshmark US. They haven't really communicated how any tarrifs imposed Tuesday will be handled. Does anyone have insight on this? Since buyers are paying for USPS labels with a shipping address based on a US PO Box, they of course will not be surcharged for tariffs. But would USPS forwarders face increased costs to export the goods to the US and therefore should Canada based cross boarder sellers expect higher service fees to get their packages across the boarder?