It all depends on how big is the network. ( and do you have own AS number, or you just want to deploy iBGP), most of the ISP do not offer iBGP
if it is small network and you looking simple LB and ISP can offer you IGP, its good to start with.
Make Sense ?
If we knew more about your environment and about your requirements we might be able to provide better answers But based on what little we know I have these comments:
1) You describe two ISP, which I assume are external connections. You do not tell us anything about your internal connections. How do you suggest that an IGP, which is an Internal Gateway Protocol, would help with failover for external connections?
2) You might achieve failover using PBR but there are at least 2 major challenges to overcome to achieve this. How do you detect the problem with an ISP to alert PBR that it should fail over. And PBR would handle failover for traffic originated inside and going outside - but how would it help with traffic initiated outside and coming to inside?
3) there are several advantages of BGP which include that it has a mechanism to detect problems with one of the ISP and to direct traffic to the other ISP. And when it automatically detects a problem with one ISP then it changes for traffic to use the other ISP for both outbound and for inbound traffic.
People usually use BGP for 2 reasons... Scalability and traffic engineering. IGP would have faster fail-over if that is your only objective. However, if it were me, I would still use BGP and incorporate BFD for fast-down detection.