Cutoff frequency on a CAN bus communication line
I have no idea what you're trying to accomplish with a filter on the CAN lines, but that's not how CAN works.  Don't do that.

What you should do is put 120 &Omega; between the two data lines at each end of the bus, and these data lines should be a twisted pair of about that impedance.  That really should have been clear from even a cursory reading of the spec.  The MCP2551 datasheet mentions 120 &Omega; terminating resistors, although in passing.

If you want to slow down the edges to reduce radiation, use the slope-limiting built into the MCP2551.  Otherwise, don't mess up the bus by trying to "filter" things somehow.