Can I also sync Leads?

The availability to sync Leads depends on whether your app has a Leads entity. The screenshot shown below is an example of the Leads entity in Copper.
When setting up a new connection, we distinguish 4 steps.
After selecting your preferred apps and finalizing the authorization process, you're able to select the contact type you wish to keep in sync.
Interested in learning more about step 1 & 2? More info can be found here.
For both applications, you can choose which contact type you wish to implement in the sync.