For information on configuring bonding on Mikrotik, just through bonding quite implement the channel switching mode is active backup.( I have checked). Offhand, create a bonding interface, add interfaces providers put the backup mode is activ, the 2 routes add a route to 0.0.0.0/0 via gates providers with different distances and check gate ping.
Next, I think, just setting up л2тп two static addresses (primary and backup ISP) on both sides.("but that is incorrect")