sorry for write an old post, but i have a similar problem…
i have a mikrotik 4011 with 2 isp
ether1 to ISP1
ether2 to ISP2
ether2 have a dynamic ip and i want configure with ovh dynhost.
on old pfsense i set simple cronjob
curl --interface igb0 --user “:” “http://www.ovh.com/nic/update?system=dyndns&hostname=<myhostname>”
and worked perfectly
now i change old pfsense with GREAT Mikrotik 
but how can i replicate that?
in fetch i can’t use --interface or similar
so i think to create an address list with domain www.ovh.com
and create a specific route to that address list (my opinion is not clear force a route with actual ip of www.ovh.com because ovh can change your ip)
how can i solve problem?
thank you