pfSense is based on FreeBSD, not Linux.
There is no such "iproute2" program for FreeBSD.
You can use pfSense's built-in features to do policy routing/load balancing in many different ways, probably better than by just using multiple routing tables.
For programs running on FreeBSD, multiple routing tables are handled by
setfib(1) but that doesn't do anything for traffic passing
through the router.