I don't have an answer to your question, but just something to consider... Big Porc is a big, long lake with multiple campsites, and in mid August, it's likely to be very busy (possibly full). If someone recommends a site at the opposite end of the lake, and you find out it's taken, you can end up doing a lot of back and forth paddling. If you have specific requirements ie. 3 tents, on a lake like this you're probably best off taking the first available site that fits those requirements. 

Parkside Bay should be a little bit better... since it's a big circle, you can paddle to the middle, use some cheap binoculars, and check out which sites are taken and which are available. You have a bit more leeway to scout out sites with lower risk of adding hours to your day.

Even saying that, obviously knowing in advance which sites can fit 3 tents would still help so you don't need to get out of the canoe at each site and find out for yourself. If you haven't already looked through the PCI reports, you should do that first: http://www.algonquinadventures.com/PCI/PCIindex.htm