Priority security in Canada (at least at YYZ) is limited to AC elites of a certain level, AC premium class passengers and certain Amex cardholders. Even UA F pax don't get priority security - so no chance of that.

Anyone telling you you won't have lounge access is simply wrong - as a *G you will have access to any *G lounge, well, in the world, so long as you are flying a *A carrier that day.