You can request circuit diversity, and ask for the circuit layout record (CLR/DLR) to verify that the paths are diverse. Standard practice is to assign circuits onto available facilities, and treat each circuit independently. So, there's no concern about whether the circuits share common facilities, unless the orders are flagged that way.
Unfortunately, future circuit grooming may result in your circuits being put onto a common path somewhere.
You can try to get the telco to guarantee diversity in writing, with financial penalties if they fail to maintain diversity. You'll need to provide backup for lost revenue, to determine how much the financial penalties should be.
By the way, there's no guarantee that intralata circuits will always be diversely routed, either. It's all dependent on the available facilities.
For interlata circuits, even if you were to go with two different IXCs, you'll need to insure that they don't share common facilities, or lease capacity on the same fiber. Years ago, a train wreck in the NY-DC corridor caused multiple carriers to experience fiber outages. Seems that one carrier trenched fiber on the right side of the tracks, and another carrier trenched fiber on the left side of the tracks. The derailment dug up both sides!
-rb