Just go and enjoy, I don't think you will have any issues with the TSA

Hear, hear.^

CORRECTION, you need to go through US CBP immigration, custom and US TSA security upon international(except Canada) arrival at all US airport even if you are doing an international onward connection.

So does the OP have to, seeing how he's flying in from Canada?

I just realized that I have never made an international-international connection at an U.S. airport so I actually have no idea whether or not this is true.

US bound flights from Canada the CBP immigration/custom are done at departing Canadian airport (preclearance) CATSA has the same security protocol and standard as TSA.

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).