See CanBus
Dedicated tool ?
CAN to USB ?
Saleae
USB, decodes frames.
not userfriendly, not tested:
STM32(F103) CAN => RS232 special fw ?
115200 baud is not too much: full CAN frames dropped if wouldn't fit into RS232 buffer.
After some time all CAN-ID-s would appear, but timing or frequency of certain ID would not be exact.