The test of post #3 was carried out using a can-bus-shield-v2 directly plugged into a UNO using the standard SPI pins 10 thru 13
it worked OK
CAN Init OK
however, today I tested your program of post #1 using a MCP2515 can module connected to a UNO (using the standard SPI pins 10 thru 13 wiring as shown in reference)
it fails
Can't init CAN
looks as though the <Canbus.h> has a problem with the MCP2515 can module
Test using the mcp_can library the MCP2515 can module works OK, e.g. running File>Examples>mcp_can>CAN_send
Entering Configuration Mode Successful!
Setting Baudrate Successful!
Initialized MCP2515
Message Sent Successfully!
Message Sent Successfully!
Message Sent Successfully!
Message Sent Successfully!
and the CANBUS shield V2 running File>Examples>mcp_can>CAN_receive
I am attaching it with jumper wires. I connected 5v and GND of shield with 5v and gnd of arduino.
Then I connected 10,11,12,13 pins of the sparkfun can bus shield v13 with pins 10,11,12,13 of the arduino.
still it is showing can't init CAN.