He wouldn't have to if he's done the preclearance in Canada. For example, for YYZ-ORD-Int'l on United, the traveler would stay airside in Terminal 1 and have no interaction with CBP or TSA there. The MCT would be identical to that of a domestic connection (or at least it should be...). Depending on where you're flying to from ORD, there might be a doc check at the gate by airline staff applying to everyone boarding the flight.

An int'l-to-int'l from somewhere with no preclearance would likely encounter the whole CBP/TSA process at the U.S. airport. I'm not familiar with every airport layout in the country, but at O'Hare this would be an arrival into T5, customs/immigration and baggage recheck in that terminal, and then a train ride (landside) to another terminal a few minutes away, and then back through TSA to your connecting gate. The UA and AA international long-hauls depart out of their regular terminals, not the international terminal (T5).