ifup brings interfaces in serial. In juju's ENI, this means that it would bring bond0 before br-bond0 and br-bond1. And since layer3, provided by br-bond1 and br-bond2 would not exist when post-up is run, post-up would fail. Because of '|| true' that would not cause ifup to fail, but it would leave the machine without routes.
I believe MAAS add 'post-up' static routes always to last interface (which is a good approach until netplan solves this). This means that juju should do the same; pick up post-up routes from the bottom of ENI and place them at the end of the last bridge it creates.
ifup brings interfaces in serial. In juju's ENI, this means that it would bring bond0 before br-bond0 and br-bond1. And since layer3, provided by br-bond1 and br-bond2 would not exist when post-up is run, post-up would fail. Because of '|| true' that would not cause ifup to fail, but it would leave the machine without routes.
I believe MAAS add 'post-up' static routes always to last interface (which is a good approach until netplan solves this). This means that juju should do the same; pick up post-up routes from the bottom of ENI and place them at the end of the last bridge it creates.