We do it multiple times per day, we are registered as a broker, have an MC, DOT, contingent cargo, surety bond, member of the TIA, a back account in the US plus pay many carriers via EFS, we also use an 800 number on the DAT board.
Dealing with US carriers is very different than Canadian carriers; there are 10x more scammers and double brokers. US carriers do not book their loads in advance and search for a load on the day of pick up.