All the security lines in Houston have a priority lane for priority passengers. In the UA terminals it will be marked Priority Access, don't think you'll be hassled if you use it. If UA prints your boarding passes to YYZ you may even have it printed on your boarding pass from your *G status.

AC is in terminal A so you will need to take a train to the terminal. There is both a fast train in the secure area and a very slow one with a tunnel outside of security that connect all the terminals. I believe international arrivals are all going to be processed in terminal E. If there is a transit security area in E I would use it to enter security, the general security line in E is always slow.

C is where United has the priority security area and it is generally very good, but will take you about 5 minutes to get between E and C outside security.

When you do get to A check in with AC at the gate so they can check your passport. There is a lounge immediately opposite their gate. If you're at all late, it might be helpful to know that the Jazz flights out of IAH have some of the worst on time performance rates.

You may get better information on the process from folks in the UA forum that have more experience as I only ever use IAH as a departure/arrival point.