If you have ever configured an IPsec VPN between a Cisco and a Juniper SRX you know it can be difficult. Actually, if you ever configured an IPsec VPN in general you know it can be a royal pain in the keester.
In any case, when you configure a Policy-Based IPsec VPN between Juniper and Cisco ISR routers, with more than one network on each side, you will find you will need an extraordinary number of policies on the SRX in order to play nice with the Cisco. If the networks allow, use IP Address Aggregation. Doing this on both sides will greatly simplify your config. In some (most?) cases you will not be this lucky.