I searched high and low and wasn’t able to find a definitive answer on whether Microsoft Windows 10 supports multipath (MPIO) over iSCSI. I found many many blog posts, articles, and press releases for Windows servers but nothing for Windows 10.
The good news is that Windows 10 supports it out of the box. You don’t have to install anything extra. Of course, the see the benefits of multipath, you will need two or more network cards. You can either bond the network cards together or set up individual routes to the iSCSI network addresses. I’ll assume that you did that already. 
This is only for new connections to your iSCSI targets. You can not retrofit multipath on to existing connections. You will need to offline the volumes, remove the targets from the favorites and then reboot.
As an administrator on your Windows 10 box:
- Launch the iSCSI initiator (Windows key and type iscsi initiator)
- Add both ip/ports to the iSCSI host in the Discovery -> Portal Groups tab
- Refresh the iSCSI targets in the Targets tab. If they aren’t shown, add them manually
- Select the iSCSI target, click connect, and select “Add this connection to the list of favorites…” (so it will automatically connect the next time you start windows) and “Enable MPIO”. Click Okay
- Select the iSCSI target, click properties. In the Portal Groups tab you should see both ip/port paths
- If you needed to offline the volumes, you will need to now online them. They should retain any drive letter assignments
