I must thank you, jggimi
I played around with pf + ECMP and actually I even have a better solution now.
My first idea was to have a single ISP as GW, and constantly monitor both of the ISPs in case one of them goes down. If it was my primary - then I wanted to change it to the other one.
But this is not worth the cost - I found found the wonderful PF's load-balancing, and now I set all my internal traffic to flow through both of the ISPs.
One problem is that if one of the ISPs looses internet connection, the load-balancing still throws half of the connections to a black hole.
Pings from the BSD itself did not work (no route to host: I have not set a primary route), so I added both of them as a ECMP route. This way I could ise the -I parameter correctly
And the ECMP is only for the pings - all other connections coming from the internal networks are explicitly routed to only one of the primary routes.
I don't know if anyone understood me, but for now I think it is a good idea
Now I see denta's answer too. AWESOME!! It looks just like the thing i was looking for, now i can experiment a lot more! thanks denta, thanks jggimi, I learned some very useful (and probably very basic also) things from you two today. Can't wait to apply this new knowledge into some pseudo-practice
I'll work & read on these topics and get back to you if I run into trouble.
Thanks!