Both will work, try near the mouths of the channels in 7-12 feet of water. Use spreaders and drift until you find em, then anchor on them. If you dont get bit in 20 minutes move around. The baitfish migration into the channels should be in full swing right now and alot of the fish follow the bait. You can still do well in the lake, try near the St Clair Light and Anchor Bay.
My dad is big on the perch fishing too. I agree with John that anchor bay can be good, sometimes even right off the Selfridge launch that time of year, but I would say that I find bigger fish out in the lake in the Sept-Oct time.
i agree with misterd. good spot there. minnows yes. spreaders yes. but sometimes they are finicky. sometimes you have to "mud em." sometimes cut off the blades from the spreader. when they are there, there;s lots of boats, & it helps to have binocs to see how others are doing (& with what). little things can make a difference.