It seems to me that you have done everything and been everywhere ... many times. By the lakefront stretch of territory you describe stretching from Rouge Beach Park to Pickering I'm assuming that you are referring to the paved waterfront trail, a route which I believe is contiguous with sections of residential streets before returning to a dedicated path. At no time have I ever suggested that this stretch of interrupted parkland was a good location to see shorebirds. I have only rarely witnessed shorebirds utilizing these beaches, and by shorebirds I mean "peeps" not gulls and terns. Once, in early June I discovered a flock of Semipalmated sandpipers on the beach at the mouth of Highland Creek. No one else seemed to notice them because unlike screeching gulls the peeps are not high decibel birds. A very large flock on the sand blend in so well that they are really only revealed by their collective movement, such as an abrupt change in foraging direction. I made my way down to the dead-end spit of sand after seeing the peeps from the bridge and approached very slowly, stopping frequently to look away from the birds and out onto the lake. Eventually I found myself standing among them and slowly crouched down and sat on the sand leaning against a large piece of driftwood that was previously delivered from Amazon just for this purpose ... that's planning ... that's forethought. Anyway, while sitting there, motionless, the sandpipers were all around me, left and right and sometimes even between my legs. It was awesome!
I've seen killdeer here and there a few times but not predictably. My best chance of seeing killdeer was on the beach at the mouth of Duffin's Creek in Ajax, also part of the waterfront trail system. This is the only location that I've seen killdeer nesting, not always successfully because there are too many people (kids) and dogs to make this a prime nesting location. I've also seen Semipalmated plover here, both breeding and non-breeding. On one occasion a small group of Whimbrel landed on this beach and paraded back and forth like picketers at a walk-out or as if they were confused.
It seems that Ashbridges Bay is still the best 'local' location for shorebirds. There have been several species visiting during August and even an American golden plover reported yesterday and today, including Baird's sandpiper, Yellowlegs, Semipalmated sandpipers, Semipalmated plovers, Dunlin a little while ago. I used to go there frequently, but not any more ... too far away from Pickering ... too much traffic ... fuel too expensive ... too many people there (dogs, joggers, cyclists). The next 5 days will be hot and humid and therefore useless for bird photography. South wind is not ideal, Labour Day festivities too wild and humidity sucks, at least for me. I hate it!
Sometimes there are shorebirds at the southern border of Cranberry Marsh (between the marsh and the lakefront) but this year there is little evidence of this particular site offering any notable shorebird activity. Even Green-backed heron and Least heron sightings are down. During previous late summers I've seen plovers, sandpipers (Semipalmated, White-rumped, Pectoral and plenty of yellowlegs. Ah, those were the days.