Cedexis now part of Citrix offers a multi-cdn product, that allows you to load balance between CDNs, check them out. I'm not sure who else is in that space, but

Cedexis now part of Citrix offers a multi-cdn product, that allows you to load balance between CDNs, check them out. I'm not sure who else is in that space, but in general it sounds like you want a multi-cdn strategy.