I want to know what would be the cause that i see TX/RX Drops
this occurs on all pppoe users on a particular site.
On router 1, isn't your static route incorrect? The one going to dst address 10.20.1.0/24. It is set for gateway ether2-PTP-Canabonsito but I think you want the gateway there to be 10.20.0.83 instead. It needs to know the next hop address and you are not supplying it.
If should use right routes:
/ip route add dst-address=172.16.1.0/24 gateway=ip of router2 Wan on first router
/ip route add dst-address=10.20.0.0/24 gateway=ip of router1 on second
Of course if you are not using nat.