No. If one compiles the micro-controller to use USB then there are no rate-limits on that connection. The available bandwidth is determined by the USB hardware (typically 12Mbit/s full-speed USB) and Linux’s USB scheduling.
I’m not sure what you are asking. As before, if the micro-controller is compiled for serial (aka UART) then the default is 250Kbit/s.
This is all related to the selections in “make menuconfig”. There is typically an option for “Communication Interface” in that menu. If one selects “CAN” then the default CANbus frequency is 1Mbit/s; if one selects “Serial” the the default is 250000 baud; if one selects “USB” then the bandwidth is determined by the usb hardware and there is no ability to impose an arbitrary rate-limit.
-Kevin