B2B marketplace where sometimes orders require 3PL (eg XPO) and sometimes orders are small enough to use normal mailing options (UPS/etc): is there a good shipping API for this or what might our logic be?

I’ve seen APIs like shippo but not sure they handle cases where we’d be shipping truckloads of pallets or containers (all domestic US to domestic US).

What sort of logic might we use for orders when doing shipping…

Something like

“If order weight is under X, use shippo. If it’s greater, use custom calculation we come up with”

Also, anywhere to find a general cost per mile?

XPO doesn’t have an integration we can use at the moment