@memaquay is probably your best place to start IMO. He's put me onto 2 so far and both were excellent.
I really liked the Steel River and the portages weren't too bad. A couple of steep banks to climb getting onto the trails around logjams and a little up & down between Diablo & Steel lakes but even with the missing beaver pond making the port into Cairngorm long ( it's about a mile), it wasn't bad. The key might be the starting point. If the access to Eaglecrest isn't viable you'd have to paddle the length of Santoy to go around the Diablo portage. (from your description, you'll want to avoid that)
Personally, I think I preferred the Marshall Lake loop but the two ports at the end are a b*tch & there's no way (that I know) to avoid the last one (pretty sure mem said you could get into Meta Lake by paddling an extra week(ish) down the Kap River).
You could put in at the bridge by Sedgman PP and paddle for a few days doing an out & back. You could even portage from Stewart to Stone Lake as that port wasn't bad at all (just swampy). The bridge to Stone & back would be some pretty country, one portage (but you'd do it twice), you could easily spend a week or more doing it and I can't think many people would be there.
As for Algonquin, I'm not sure how often Drew (
@Algonquin lakes) checks in here but he's got an awesome website and has covered quite a lot of the park in the past 8 years. Lots of info, campsite ratings, etc. Bonus: he's a really nice guy too.
(edit: I see that he was last on here in Sept of '24 so you might want to pm him or contact him thru his website.)
Good luck & hope you can get back to it.