http://www.united.com/page/article/0,6722,1113,00.html

AC has the best gates for connecting to virtually any UA or UX flight at ORD. AC arrives in T2 at E1 or E2. You walk right off the plane and you're in UX-land (turn right) or over to T1 (turn left and a short hike to concourse B -- or turn right and look for the shuttle to concourse C -- gate C9 -- at E3). Monitors are right out front, so all you have to do is look for the gate assignment. Your bags *should* connect, so long as AC sees your whole itinerary -- just check that when you check bags.

You should be able to get to the end of T2 (gate F14) within 5-10 minutes and anywhere in T1 within 15 minutes at a very reasonable pace. You don't have to take the tram between terminals -- you can walk or take a shuttle bus from gate E3 to gate C9.

Just be real careful about following signs. You can get from T2 to T1 without ever going through security again. Just watch the signs. I have seen entirely too many people follow the herd and find themselves in the ticket lobby or at baggage claim looking for gate C20.

You'll preclear US Immigration and Customs in Canada, so your flight is treated like a domestic flight.