First, the governments are not interesting in enforcement of load brokers (Provincial, Canadian or US). Second, the US surety bond is only there to "protect" unpaid carriers to the value of the bond, $10,000 minimum (and usually maximum). Thirdly, the bond provides no protection against any other claims.
Many prudent brokers will carry cargo contingency insurance which addresses Moose's last paragraph, but it is not a license requirement. It also will revert back to the actual carrier's cargo insurance maximum, so if you have a $400,000 contingency cargo limit and use a carrier with only $100,000 cargo limit, your secondary coverage may stop at $100,000.00 and not $400,000 as you may think. Also if you are a carrier who also brokers freight, and you did not touch the freight, then only the actual carrier's cargo insurance responds - you do not have coverage under your own cargo plicy unless you have a contingency cargo covergae ryder.
I have not addressed the PL and PD liability of brokers where the actual carrier ends up in an accident - as in the $24 million jury award to the plaintiffs in the CH Robinson (as broker) judgment.
Finally