Active-passive setups can be achieved with VRRP, which is also first-hop redundancy. It is configured like this:
Router1
/ip address add interface=ether1 address=192.168.1.2/24 disabled=no
/interface vrrp add interface=ether1 vrid=10 priority=50 preemption-mode=no disabled=no name=ether1.vip
/ip address add interface=ether1.vip address=192.168.1.1/32 disabled=no
Router2
/ip address add interface=ether1 address=192.168.1.3/24 disabled=no
/interface vrrp add interface=ether1 vrid=10 priority=30 preemption-mode=no disabled=no name=ether1.vip
/ip address add interface=ether1.vip address=192.168.1.1/32 disabled=no
If you want an active-active setup, the only way is to run a dynamic routing protocol on your hosts, such as ospf, rip or bgp.