Connecting Can Bus Debugger with Arduino Uno
CAN is a 60Ohms Impedance both sides/ends terminated Bus (120Ohm resistors)
At least that's the most common physical Layer approach.
borrowed from Wikipedia:

Wikipedia on CAN
This one - in the wikipedias linklist - has some nice descriptions
https://web.archive.org/web/20161213185005/http://inst.cs.berkeley.edu/~ee249/fa08/Lectures/handout_canbus2.pdf
This has some useful info on the common connectors.
http://www.interfacebus.com/Can_Bus_Connector_Pinout.html

I also always forced my superiors to buy galvanic isolated CAN sniffers like that
https://www.kvaser.com/product/kvaser-leaf-pro-hs-v2/
or stuff from vector informatik (used to sell brand labelled Kvaser a lot...)
You will have much less problems with levels, GND's etc... they just work in most cases

Edit01:
So at first sight, it seems the Adurino shield can be configured to standard sub-D layout plus already is terminated (guess the &quot;wrong&quot; value of 100 is to get it also work with OBD-II)

The USB Peak Can also supports the standard Layout

So thats fine, and last

The USB Peak Can also has an option for termination, but I would just solder a 120 Ohm resistor + a switch to pins 2 and 7 of the Adurino shields sub-D connector. So you can turn it on an off as needed